perf: reuse Postgres pools for connect

[larimonious]

Summary

• make std/db/postgres.connect(url) reuse a process-local shared pool keyed by connection string
• keep each connect(url) call returning a fresh logical handle, with transaction state isolated per handle
• change close(handle) to invalidate only that logical handle while keeping the shared URL pool cached
• remove the now-stale postgres_connect_in_function lint and update docs/generated stdlib references

App compatibility scan

Scanned Larri-owned ntnt apps/repos under /home/larimonious/apps and /home/larimonious/repos for std/db/postgres imports and aliased calls.

Findings:

• Most apps use module-scope connect() handles already: larri-net, ntnt-lang-org, TAP, Running Wild, Panamera Hub, site templates, etc.
• Larri Dashboard has one request-local pg_connect/pg_close path in lib/dashboard_signals.tnt; this PR directly fixes that churn.
• Benchmark/demo code intentionally does request-local connect → query → close; this now hits the shared pool fast path.
• Only transaction usages found were ntnt examples / worktree examples; transaction state remains per logical handle.
• No app relied on close() destroying the underlying URL pool.

Verification

• cargo build --profile dev-release
• cargo test -q — 1165 unit tests plus integration suites passing
• ./target/dev-release/ntnt validate examples/ — all 57 examples valid, existing 6 warnings
• ./target/dev-release/ntnt lint examples/ — existing warnings/suggestions only
• Docker Postgres smoke test:
  • 50 repeated connect(url) calls stayed at activity_count=1
  • close(handle) invalidated the logical handle with Invalid or closed database connection
• git diff --check

[greptile-apps]

Greptile Summary

This PR changes Postgres connections to reuse shared pools while keeping logical handles separate. The main changes are:

• Shared Postgres pools keyed by normalized connection strings.
• Per-handle tokens for close and transaction validation.
• Updated close behavior that invalidates only the logical handle.
• Removed the stale request-local Postgres connect lint.
• Updated docs and tests for the new pooling model.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

Important Files Changed

Filename	Overview
src/stdlib/postgres.rs	Adds shared pool reuse, normalized pool keys, per-handle tokens, and handle validation for close and transaction operations.
src/main.rs	Removes the lint that warned about calling Postgres connect inside functions.
tests/type_checker_tests.rs	Removes tests for the retired Postgres connect lint.
docs/DEPLOYMENT_GUIDE.md	Updates deployment guidance to describe shared Postgres pool reuse.
docs/RUNTIME_REFERENCE.md	Clarifies the shared Postgres pool behavior for NTNT_DB_POOL_SIZE.
docs/STDLIB_REFERENCE.md	Updates the Postgres stdlib reference for shared pools and logical handle close semantics.
docs/runtime.toml	Updates runtime metadata for the revised Postgres pool behavior.

_{Reviews (4): Last reviewed commit: "fix: enforce Postgres handle tokens" | Re-trigger Greptile}