Read whole numbers from computer env, and keep the port in range

[Ayush7614]

What this changes

Fixes #497. The computer's env reader accepted anything Number called finite and positive:

• PORT=80.5, NAVIGATION_TIMEOUT_MS=0.5, ACTION_TIMEOUT_MS=0.1, COMPUTER_MAX_BROWSERS=2.5, COMPUTER_BROWSER_IDLE_MS=0.5 were all returned verbatim. A fractional port misbound at boot, a fractional timeout fired before any action could finish (surfacing as 502s reading as a broken computer), and a fractional cap reached eviction math. PORT=99999 parsed fine and then misbound — a deployment failure instead of the documented fallback.
• numberFromEnv now takes whole numbers on sight (trim + /^\\d+\$/ + parseInt, the same rule as the supervisor's listenPort), with optional min\)/maxfor settings with a range.PORTrides{ min: 1, max: 65535 }; timeouts and counts stay unbounded above, like before. Zero semantics unchanged: COMPUTER_BROWSER_IDLE_MS=0` still keeps browsers resident, and the empty-string-means-unset rule the function exists for is untouched.

Where it runs

The computer process holding one Bot browser, at env read. Same fallback on every computer.

• New state that outlives a request? None. Per-process env parsing.
• What happens on the second replica? Same fallback on every computer: pure function of the environment. No cross-computer coordination.
• Anything serialised? No.
• Anything fanned out to a browser? Timeouts reach Playwright only after parsing, on the computer that owns that browser — and now only as whole numbers.
• New listener, port, or schedule? No. The port this process serves on is unchanged when the variable is well-formed.

Postgres is already there and is the default answer to all of the above: nothing here needs it.

Boundary and audit

• Every acting call still goes through the gateway: resolve, decide, audit, then act. The computer holds no policy engine; this checks well-formedness only, same as the existing navigate/timeout/scroll checks.
• New refusals and new failures each write a row. N/A on this process: fallbacks are startup config answered with the documented default, matching the existing behaviour.
• Nothing new is trusted from the client that the server can resolve itself. Stricter: fewer shapes reach Bun.serve/Playwright/eviction math.

Changelog

• A line in CHANGELOG.md under Unreleased: computer env validation entry.

Proof

• bun test agent-computer/tests/number-from-env.test.ts: 28 pass (11 pre-existing + 17 new: 6 fractional/sci/hex fallbacks, large-int passthrough, zero-off fraction, 4 in-range ports, 6 out-of-range/non-whole fallbacks).
• bun test in agent-computer: 306 pass, 15 skip, 0 fail across 21 files.
• bun run typecheck in agent-computer (after bun install --frozen-lockfile, as CI does): clean.
• bunx biome format + bunx biome lint --error-on-warnings on touched files: clean.

[davidmckayv]

Deep-reviewed clean (validation, no secret leak, fail-closed, agrees with existing layers). CI green.