docs(release): reconcile README, SPEC, roadmap, and release notes for v0.3.0

[CrisSTEM]

Summary

Reconcile the repository documentation with the delivered v0.3.0 ingestion baseline.

The runtime is no longer a catalog/bootstrap-only foundation: fetch is implemented, ingestion observations are persisted in SQLite, and GitHub/news/changelog source support is real. This PR updates the docs so they describe the implemented runtime rather than the earlier pre-implementation contract freeze.

Linked issue(s)

• Closes docs(release): reconcile README, SPEC, roadmap, and release notes for v0.3.0 #34

Milestone fit

This PR completes the documentation/release alignment portion of the v0.3.0 milestone.

It keeps the repository honest about what is already delivered:

• fetch CLI execution
• persisted fetch_runs, metric_snapshots, and content_items
• GitHub/news/changelog ingestion support

It also keeps the milestone boundary explicit by documenting that scheduler, alerts, API, and dashboard work remain deferred.

What changed

• updated README.md with a reviewer-usable fetch quickstart
• reconciled SPEC.md, docs/architecture.md, docs/configuration.md, docs/data-model.md, and docs/reference-dataset.md with the implemented ingestion runtime
• aligned docs/roadmap.md, CHANGELOG.md, and drafted docs/releases/v0.3.0.md
• documented the current Google News RSS provider choice and optional GITHUB_TOKEN behavior
• documented current reviewer/runtime caveats such as anonymous GitHub API rate limits and the current reseed-before-fetch CLI behavior

Out of scope

• scheduler runtime and long-running orchestration
• delta detection, alert evaluation, and candidate discovery
• HTTP API handlers and dashboard pages
• app-store and social fetchers
• owner-scoped github.contributors aggregation
• runtime behavior changes beyond documentation reconciliation

Validation

Mark what you actually ran:

• python3 ./scripts/trim-whitespace.py --check
• go vet ./...
• go test ./...
• make ci
• Manual CLI verification was performed if runtime behavior changed

Manual verification performed:

go run ./cmd/signalscope check-config --config configs/demo/blockstream  
go run ./cmd/signalscope seed-demo --config configs/demo/blockstream --db /tmp/signalscope-v0.3.0-news.db  
go run ./cmd/signalscope fetch --config configs/demo/blockstream --db /tmp/signalscope-v0.3.0-news.db --source news_rss  
go run ./cmd/signalscope fetch --config configs/demo/blockstream --db /tmp/signalscope-v0.3.0-github.db --source github  
go run ./cmd/signalscope fetch --config configs/demo/blockstream --db /tmp/signalscope-v0.3.0-changelog.db --source changelog  

Manual verification notes:

• news_rss succeeded and populated fetch_runs, metric_snapshots, and content_items
• anonymous GitHub-backed runs hit GitHub API rate limits in the reviewer environment
• those failures were still recorded correctly in fetch_runs
• changelog verification showed mixed success/failure behavior, with RSS-backed bindings succeeding while GitHub-backed release bindings were rate-limited

Documentation impact

• No docs update needed
• README.md
• SPEC.md
• docs/
• repository governance docs (AGENTS.md, CONTRIBUTING.md)
• CHANGELOG.md
• release notes

Reviewer focus

Please review the docs against the actual runtime behavior in particular for:

• the reviewer quickstart and SQLite inspection path in README.md
• the documented fetch semantics, especially reseed-before-fetch behavior
• the GitHub/news/changelog source notes and optional GITHUB_TOKEN path
• the distinction between delivered ingestion and deferred scheduler/alerts/API/dashboard work

Auditability checklist

• Branch name follows project convention
• PR scope matches the linked issue and milestone
• Commits were pushed progressively, not as one final dump
• Relevant tests were added or updated for behavior changes
• No secrets or sensitive credentials were introduced
• Deferred follow-up work is documented explicitly
• Unimplemented work is not implied as completed

Notes for merge

Preferred merge method:

• Issue PRs: Rebase and merge
• Release aggregation PRs: Merge commit
• Use Squash and merge only when the branch became noisy and preserving intermediate commits no longer adds value