feat(entrypoints): schema, Neo4j projection and the level-free pass skeleton

[rahlk]

Closes #153. Unit 1 of the entrypoint spec (#150): the contract, before any detector exists.

The fields were de-advertised in #60 because nothing populated them. This lands their shape so they
exist at every -a and a consumer can already tell "no entrypoints" from "no pass ran". Detection —
the framework gate, the rules file, the matchers — is units 2-5 (#72).

What this adds

• TSEntrypoint / TSEntrypointReport, mirroring PyEntrypoint / PyEntrypointReport field for field
• entrypoints: [] and is_entrypoint: false on every callable and every class, stamped by a
  per-run pass — like heritage, so the cached tree stays free of them and the wire always carries them
• entrypoint_report on the application root, empty
• Neo4j, exactly as python projects it: is_entrypoint / entrypoint_frameworks on :TSClass and
  :TSCallable; on :TSApplication, entrypoint_frameworks plus entrypoint_report_json as
  sorted-key JSON (Neo4j has no map type; python encodes it the same way, so the two diff)

Two decisions worth a look

Class only, never interface/enum/alias/namespace. Python stamps PyClass; nothing else can be an
entrypoint. The field is declared on TSType (optional) but the pass stamps classes, and Neo4j declares
it on :TSClass only — so a dead is_entrypoint: false never appears on an interface. The test asserts
the absence, not just the presence, and a mutant that drops the guard fails it.

Per-run pass, not builder defaults. #60 noted the builders used to hard-code entrypoints: [].
Stamping in a pass instead means the cache never holds a per-run layer, and the test proves it: L1 runs
cold, then L2–L4 run against the warm cache (whose modules lack these fields) and all four are
byte-identical.

Verification

• bun test — 247 pass, 0 fail (5 new). The root-envelope key list in schema-v2.test.ts gains the
  one new key — that additive-contract gate caught it first, as intended
• Mutation-checked — removing the class-only guard fails the interface-absence test
• Container tests run — 4 pass against live Neo4j
• schema.neo4j.json regenerated; SCHEMA_VERSION unmoved (chore(schema)!: collapse the schema version back to 2.0.0 #144); typecheck clean

Honest caveat

The report is honest-but-empty until unit 2: frameworks_detected: [] here means "no gate ran", not
"no frameworks present". Unit 2 is what makes that distinction real, and it is the next PR.