bindings: document schemas, additive telemetry-path export, deprecation + staleness/arg coverage

[andrescera]

What

Documentation, an additive root re-export, and deprecation/coverage hardening for the
@ceralive/srtla TypeScript bindings. No behavior change to the bindings' runtime
surface; no C/C++ source changes.

• Schema docs: JSDoc on the sender/receiver Zod option schemas and .describe() on
  their port (and related) fields, so the CLI mapping is self-documenting.
• Additive root export: senderTelemetryPath is now re-exported explicitly from the
  package root (it was already reachable via export *; this makes it discoverable
  without the ./telemetry subpath).
• Deprecation normalization: every retired C-sender export now carries the uniform
  tag @deprecated Use `@ceralive/srtla-send` instead. (previously a mix of /sender
  and /telemetry subpaths).
• New tests:
  • deprecation-coverage.test.ts — a symbol-level @deprecated enumeration over the
    C-sender export files (parses each export and inspects the JSDoc block directly above
    it; not a whole-file grep -L). Dropping the tag from one export fails the test and
    names that export.
  • export-stability.test.ts — pins the full frozen runtime export set and confirms the
    additive senderTelemetryPath is callable from the root.
  • telemetry/staleness-boundary.test.ts — boundary coverage with hardcoded snapshot
    ages (4999/5000/5001 ms) so it genuinely pins the 5000 ms window.
  • sender/stats-file-arg.test.ts — --stats-file emission from buildSrtlaSendArgs,
    tied to senderTelemetryPath(listenPort), plus the omitted-when-unset case.

The tracked dist/ output is rebuilt to stay in sync with src/.

Why

The bindings API is frozen (srtla AGENTS.md: "existing exports frozen") but under-
documented, and the C srtla_send is retired in favour of @ceralive/srtla-send
(ADR-003). These changes make the deprecation story uniform and machine-checked, document
the option schemas for consumers, and lock the telemetry staleness/arg behavior with
falsifiable tests — all additively, without touching the frozen export set.

How to verify

• cd bindings/typescript && bun x tsc -p tsconfig.json --noEmit → clean.
• bun test → 136 pass / 0 fail.
• Falsifiability (both confirmed locally, then reverted):
  • Lower SENDER_TELEMETRY_STALE_MS to 4999 → the staleness boundary test fails on the
    age-5000 snapshot.
  • Remove @deprecated from one C-sender export → deprecation-coverage.test.ts fails and
    names that export (e.g. buildSrtlaSendArgs (line 18)).
• C side unchanged: cmake -B build && cmake --build build && ctest --output-on-failure
  → 186/186 pass.

Risks

Low. No export added/removed/retyped (.describe() returns the same ZodType, so
z.input/z.output are unchanged); edits are JSDoc/comment-only plus four new test files.
The 5000 ms staleness threshold is unchanged.

Note on the staleness boundary: the committed reader is now - last_updated_ms > 5000, so
age 5000 ms is inclusive-fresh and 5001 ms is the first stale age (locked by the existing
index.test.ts boundary test and the C header). The new test asserts that implementation-
true boundary; the plan's "now-5000 → null" wording is an off-by-one against the frozen
> semantics and was intentionally not "fixed" (doing so would flip >→>=, break the
existing test, and change the threshold behavior — all out of scope).