AK-508: ignore .architect/ and .reviewer/ agent findings dirs

[benw5483]

Summary

Coding-agent review rounds write .architect/ and .reviewer/ findings directories at the repo root of every worktree. They hold internal run identifiers and raw review commentary. This repo didn't ignore them, so the standard recovery move when a build goes sideways (a broad git add -A) could sweep them straight into a PR.

This appends a five-line block to the existing .gitignore. The comment above the two entries is deliberate: it tells the next person what these directories are, so they don't get deleted later as unexplained noise.

Nothing matching was already tracked

Checked before committing:

$ git ls-files | grep -E '^\.(architect|reviewer)/'
(no output)

Empty, so no findings file is already committed here and this change is purely preventive. Had it come back non-empty, untracking those files would've been a separate and much more careful job than adding an ignore rule.

The diff is additive only

git diff --numstat reports 6 0 .gitignore: six lines added, zero removed. Nothing existing is deleted, reordered, or reformatted, and no other file in the repo is touched.

Test plan

• git diff --numstat on this PR shows additions only, against .gitignore alone.
• mkdir -p .architect .reviewer && touch .architect/x.json .reviewer/x.json && git status --porcelain leaves both directories out of the output.
• git check-ignore -v .architect/x.json .reviewer/x.json attributes the match to the two new .gitignore lines.

All three ran locally on this branch and passed.

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Generated by the operator's software factory.
• City: factory-main · Agent: local-core.builder-4
• On behalf of: @benw5483