feat: Replace Example[T] generation with markdown-based example docs

[EspenAlbert]

feat: Replace Example[T] generation with markdown-based example docs

What

Overhaul pkg-ext's example documentation system: remove the Example[T] Pydantic subclass generation machinery and replace it with markdown-based example docs validated by pytest-examples. Also clean up dead code left behind and add changelog tooling for rebasing and PR stacking.

Changes

t07-40: Remove Example[T] generation

• Deleted example_gen.py module and its tests
• Removed gen-examples CLI command
• Removed examples_enabled, examples_exclude config fields and all associated filtering/rendering methods
• Removed examples_file_path from PkgSettings and generate_examples_for_groups from pre_change workflow
• Kept examples_include on GroupConfig as the source of truth for which symbols need example docs

t07-41: Add gen-example-prompt and check-examples commands

• gen-example-prompt: builds an AI prompt from API dump data (signatures, docstrings, related types, test code) for symbols missing example docs. Copies to clipboard via pbcopy. Supports --group filter.
• check-examples: verifies every symbol in examples_include has a corresponding .md file under docs/examples/{group}/. Exits non-zero on missing files. Skippable via SKIP_EXAMPLES_CHECK=1.
• Business logic in examples.py, CLI wiring in cli/example_cmds.py

t07-42: Link example files from generated docs

• Generated group index pages include example links with descriptions parsed from YAML comment headers
• Added parse_description_comment; threaded example context through render_group_index and generate_docs

t07-43: Remove gen_tests command and test_gen module

• Deleted test_gen.py, test_gen_test.py from generation/
• Removed gen_tests CLI command, its registration in base_commands.py, and its re-export in generate.py
• Removed generate_tests_for_groups() from workflow_cmds.py and filter_group_by_examples_include() from examples.py
• Removed test_file_path() from PkgSettings
• Cleaned .groups.yaml owned_refs and unused imports

t07-44: Auto-remap changelog SHAs after rebase

• Stale SHA detection runs automatically at the start of add_git_changes before the commit loop
• Auto-remap matches stale FixAction entries to new commits by exact commit message, using timestamp proximity as a tiebreaker
• Interactive fallback for unmatched entries (squashed/amended/dropped commits)
• Bot mode inherits raise_on_question behavior -- auto-matched SHAs are applied silently, unmatched entries trigger NoHumanRequiredError

t07-45: Add change-base command and pre-commit base-branch validation

• change-base CLI command -- diffs .changelog/ between the new base and HEAD, finds changelog files belonging to other PRs, consolidates their actions into the current PR's file, and deletes the originals
• Pre-commit validation -- detects foreign changelog files relative to the PR's base branch and fails with an actionable error message pointing to change-base

t07-46: Add examples to mkdocs nav and inline per-symbol links

• Example pages now appear in the mkdocs nav sidebar under an "Examples" sub-nav within each group that has examples
• Replaced the disconnected "Examples" table at the bottom of group index pages with per-symbol - [Example: {description}]({link}) lines rendered directly after the source link
• Flat nav groups (no complex symbols) automatically become nested when they have examples
• _render_nav_yaml supports 3-level nesting for the Examples sub-nav

Why

The Example[T] Pydantic subclass approach coupled code examples tightly to the generation pipeline. Replacing it with standalone markdown files validated by pytest-examples gives better authoring ergonomics, simpler tooling, and docs that link directly to example files. The changelog improvements (SHA remapping, change-base) fix real pain points when rebasing and stacking PRs.

Reviewer notes

• Breaking: gen-examples and gen_tests CLI commands are removed. No known callers outside manual use.
• Breaking: examples_enabled and examples_exclude config fields in pyproject.toml are no longer recognized. Migrate to examples_include only.
• Docs rendering change: SymbolContext.has_examples is removed -- symbols that previously got their own page solely because they had examples will now be inlined on the group index page (unless they have env vars or meaningful changelog changes).
• Docs rendering change (t07-46): The bottom-of-page "Examples" table (render_examples_section) is removed. Example links now appear inline next to each symbol's source link, with the description from the example file's YAML comment header.
• Nav type change (t07-46): NavItem children can now contain nested lists (for the Examples sub-nav). _render_nav_yaml handles 3-level YAML indentation. NavChildItem type alias added.
• Example file paths use the symbol name as-is (CommentConfig.md), not snake_case.
• clipboard.py duplicates the pbcopy pattern from adoc to avoid a cross-package dependency.
• YAML changelog files are updated via regex-based string replacement to avoid re-serialization side effects. CHANGELOG.md regenerates from YAML at release time.
• find_changelog_files_in_diff shells out to git diff --name-only {base}...HEAD -- requires the base ref to be locally available. In CI this is always true; locally it may need a git fetch first.
• Pre-commit validation only runs when gh pr view returns PR info (CI context). Local dev without an active PR skips the check.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 81.02190% with 78 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.84%. Comparing base (3b5fd97) to head (2c37386).
⚠️ Report is 59 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg_ext/_internal/changelog/committer.py	44.44%	25 Missing ⚠️
pkg_ext/_internal/cli/workflow_cmds.py	23.33%	23 Missing ⚠️
pkg_ext/_internal/cli/example_cmds.py	37.50%	20 Missing ⚠️
pkg_ext/_internal/examples.py	92.62%	9 Missing ⚠️
pkg_ext/_internal/changelog/change_base.py	97.22%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #19      +/-   ##
==========================================
+ Coverage   77.77%   79.84%   +2.07%     
==========================================
  Files          76       80       +4     
  Lines        4818     4982     +164     
==========================================
+ Hits         3747     3978     +231     
+ Misses       1071     1004      -67     

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