Release-ready: working demo gif, fix-mode polish, piped-input lands in the model

[FrancoisChastel]

Summary

Final pre-release polish. Two layered changes:

1. Release-readiness docs pass (75b46a6)

• README install is now three concrete steps (tool → model → go) with the previously missing `huggingface-cli download` and the `SHELLLM_AUTOSTART=1` no-babysit path.
• Formula caveats / test cover the current entry points (`shellllm-recall`, `shell_context` module, the `,,` glyph) and the model-download step.
• HOMEBREW.md user instructions match.
• AGENTS.md describes the current five-glyph surface and adds the terminal-context ladder to the load-bearing invariants.
• Last stale `?:` reference in `, --help` updated to `???`.
• `pyproject.toml` + `init.py` bumped to 0.2.0.

2. Fix-mode polish, piping that actually works, real demo gif (`c674df8`)

Three real bugs caught while rendering the demo, all fixed:

Bug	Fix
`,,` continued the prior `,` thread, refining the last question instead of repairing the last command	`--fix` archives + resets the comma session before running
`,,` proposed commands that operated on cwd files (`python3 build.py`) instead of fixing the failed command	Dedicated `_fix_system_prompt()` pins the model to REPLACEMENT commands; cwd-listing context block skipped in fix mode (the model was anchoring on filenames there)
`make 2>&1 | ? what broke` came back with "I don't see any input attached"	Piped content now rides on the user message (with framing) — local 27B-class models reliably ignore system messages saying "this IS the input"

Plus:

• Previous-command capture switched from `fc -ln -2 -2` (unreliable inside function bodies) to `$history[$HISTCMD-1]` + a `precmd` hook for exit status. Robust across `HIST_IGNORE_DUPS` / `SHARE_HISTORY`.
• `demo.tape` rewritten with model warmup, `Wait+Screen` sync, and the new `,,` and piping beats. The rendered `demo.gif` is committed and embedded in the README hero.

Test plan

• 257 tests pass (`pytest -q`) — new coverage for `,, ` fresh-session, `--fix` prompt contract, piped-block phrasing
• `ruff check` and `ruff format --check` clean
• CI green
• Manual: `,,` on `gti status` proposes `git status` as the first item (shown in demo.gif at ~30s)
• Manual: `python3 build.py 2>&1 | ? one line: what is broken` produces an actual diagnosis (shown in demo.gif at ~60s)
• Before merging: brew install --build-from-source ./Formula/shellllm.rb and brew test shellllm