docs: remove advertising proof gallery and campaign guide

[Coding-Dev-Tools]

Summary

Removes the retired advertising surfaces from the repository:

• Deletes docs/advertising/ (index.html, campaign.md) and its dedicated test tests/test_advertising_assets.py
• Removes the "Grounded, not guessed" proof-gallery tagline and its two links from the README
• Adds .gitignore rules for two local session-transcript prompt filenames that inspect private ~/.commandcode/ session data, using the repo's existing character-class casing convention for private working papers

Verification

• pytest tests/test_benchmark_evidence.py tests/test_release_infrastructure.py tests/test_dashboard_vendor_assets.py tests/test_skill_package.py -q — 64 passed (includes the em-dash punctuation contract and registered benchmark-string gates flagged during review)
• ruff check . — clean
• README rebuilt from pristine upstream content with only the tagline removed; verified no BOM, no encoding drift, all arrows/checkmarks/tree glyphs intact

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[Coding-Dev-Tools]

Closing as superseded: the advertising-gallery removal already landed on main via #163 (35b222b). This branch also deletes .gitignore and conflicts with main; nothing unique to merge.

[Coding-Dev-Tools]

Reopening: the supersession rationale no longer holds after conflict resolution on the branch. What changed since closure: (1) Branch rebased onto current main 35b222b - overlapping deletions auto-resolved in favor of #163; (2) the accidental wholesale .gitignore deletion at old tip 6bd6ead was dropped entirely; (3) surviving unique delta 5f9f228: .gitignore now uses character-class patterns covering both private session-transcript prompt filenames, a strict superset of the literal-name rules #163 added, so mixed-case variants cannot slip through on case-insensitive machines - verified locally via git check-ignore against exact/mixed/ALL-CAPS variants; (4) local verification ruff clean and PR 64-test verification set passes. CI will run against new head; merging via rebase once green.

[Coding-Dev-Tools]

Reopening: the supersession rationale no longer holds after conflict resolution on the branch.

What changed since closure:

• Branch rebased onto current main (35b222b). The overlapping deletions (docs/advertising/, tests/test_advertising_assets.py, README tagline) auto-resolved in favor of chore: remove advertising gallery and purge local transcript prompts #163.
• The accidental wholesale .gitignore deletion at the old tip (6bd6ead) has been dropped entirely.
• Surviving unique delta (5f9f228): .gitignore now uses character-class patterns (/[Pp][Rr][Oo][Mm][Pp][Tt]_...) covering both private session-transcript prompt filenames — a strict superset of the literal-name rules chore: remove advertising gallery and purge local transcript prompts #163 added, so mixed-case variants can't slip through on case-insensitive machines. Verified locally via git check-ignore against exact/mixed/ALL-CAPS variants.
• Local verification: ruff check . clean; the PR's 64-test verification set passes.

CI will run against the new head; merging via rebase once green.