chore(eslint): enforce kebab-case filenames, purge convention prose

[hercemer42]

What

Encodes the one enforceable agent-nodejs convention as an ESLint rule (from the PRD-711 conventions analysis) and drops the unmeasurable clean-code prose from CLAUDE.md.

• unicorn/filename-case — error, kebab-case. Prevents a real bug class: macOS (case-insensitive) vs Linux CI (case-sensitive) import-path mismatches. Relaxed via ignore-globs for the generated ANTLR parser (can't rename), snake_case datasource-demo-fintech fixtures, and _-grouped test files — every existing violation is covered, so CI stays green while new violations are blocked.
• One new devDep, pinned for ESLint 8: eslint-plugin-unicorn@^48.0.1 (later majors require ESLint ≥8.56).
• CLAUDE.md: purged DRY/KISS/YAGNI, single-responsibility, AAA, pure-functions, comments-why-not-what, descriptive-names — generic prose that carried no repo-specific information.

Why cutting the prose costs the models nothing: CLAUDE.md is injected into every agent session, so each line spends context budget. DRY/KISS/YAGNI/AAA-style advice is the most over-represented guidance in any model's training data — models (and experienced devs) already default to it unprompted, so restating it changes zero behavior. The repo's own measurements confirm the habits hold without the prose (median 8 lines/function, 99.9% of ~46k functions ≤4 params, kebab-case at 846/849). Meanwhile every generic line dilutes the doc's real job: carrying the Forest-specific signal a model can't guess — architecture, workflows, and the conventions the linter actually enforces.

What was considered and dropped

Three advisory rules (max-params: 4, max-lines-per-function: 50, promise/prefer-await-to-then) were measured (46 / 131 / 16 existing src violations) and initially added as warn — then removed: CI has no --max-warnings gate, so a warning nobody fails on is dormant documentation, not enforcement. They can return as error + bulk suppressions after the ESLint 9 upgrade (blocked today by airbnb-config deprecation, separate ticket). max-lines-per-function is the least likely to return as-is: the length distribution is bimodal (median 8, but a legitimate tail of long-declarative route handlers and decorator wiring), so a blunt line count can't separate justified outliers from real smells — that's per-function judgment, which belongs in the conventions corpus, not lint.

Notes for reviewer

• Config + docs only — no production code touched.
• Local lint on an unbuilt worktree shows 4 pre-existing @typescript-eslint/no-throw-literal errors in agent/src/routes/.../action-authorization.ts; this is a type-resolution artifact of the unbuilt tree (CI builds before linting and is clean). Unrelated to this change.

Refs PRD-759

Note

Enforce kebab-case filenames via eslint-plugin-unicorn and trim CLAUDE.md conventions

• Adds eslint-plugin-unicorn and enables the unicorn/filename-case rule (kebab-case) in .eslintrc.js, with overrides disabling it for generated ANTLR parser files, demo fixture packages, and test directories.
• Removes prescriptive prose from CLAUDE.md (DRY/KISS/YAGNI, naming, size, parameter, and AAA test bullets), replacing it with a note that ESLint owns mechanical rules and the remaining points are judgment calls.

^{Macroscope summarized 99443ce.}

[linear-code]

PRD-759

[qltysh]

Coverage Impact

This PR will not change total coverage.

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[hercemer42]

Claude Fable 5 (claude-fable-5) — review + scope history

1. A /validator pending review found one Preferential issue (max-lines-per-function counted comment/blank lines); fixed in 29e9691d.
2. Scope was then cut in 84fa5312: all three advisory warn rules (max-params, max-lines-per-function, promise/prefer-await-to-then) removed — CI has no --max-warnings gate, so ungated warnings are dormant documentation, not enforcement. The pending review was discarded as moot (its finding anchored to a removed rule).

Final scope: unicorn/filename-case (error, kebab-case, ignore-globs for generated parser / demo fixtures / tests) + the CLAUDE.md prose purge. See the PR description.

CI note: the workflow-executor test failure (AI payload bounding (HasMany)) is pre-existing on main — the run for b4e7fcd2 (this branch's fork point) fails the same job. The three "failed" datasource jobs are fail-fast cancellations; every lint step that ran on this PR passed.