fix(rtk): use prompt-level Codex guidance without a hook

[shunk031]

Why

RTK setup must install the pinned binary and disable telemetry, while Codex integration should follow RTK's official integration contract. Upstream documents Codex support as prompt-level guidance through AGENTS.md, with no programmatic hook. The custom public Codex hook duplicated that contract and introduced an unnecessary runtime bridge.

What Changed

• Restore the complete RTK setup path: pin RTK 0.42.4 in mise and invoke install/common/rtk.sh from the managed run-after template.
• Restore the Claude/Gemini source wiring and settings needed by the supported RTK integrations.
• Keep RTK_TELEMETRY_DISABLED=1 on both supported global RTK initialization calls.
• Restore static RTK guidance in home/dot_config/codex/AGENTS.md for rtk prefixes, rtk gain, and rtk proxy.
• Document in install/common/rtk.sh that Codex uses managed AGENTS.md guidance instead of a generated @RTK.md reference or programmatic hook.
• Remove the custom public Codex hook files and hook-specific test; retain coverage for setup wiring, guidance, and telemetry behavior.
• Do not add a private Codex hook or invoke rtk init --codex; the public managed source remains the authoritative guidance.
• Consulted upstream: RTK Codex integration README, supported-agents documentation, and the Codex initializer implementation.

Validation

Check repository setup and all configured pre-commit checks.

make setup
prek run --all-files

Check shell syntax, shellcheck diagnostics, and repository-style formatting.

bash -n install/common/rtk.sh
shellcheck install/common/rtk.sh
shfmt --indent 4 --space-redirects --diff .

Validate the staged JSON sources and patch formatting.

git show :home/dot_config/antigravity-cli/settings.json | jq empty
git show :home/dot_config/claude/settings.json | jq empty
git diff --cached --check
git diff --check

A direct initialize_rtk smoke check verified both telemetry-disabled RTK init calls and confirmed that no Codex initialization is invoked.

Local Bats was intentionally not run, per repository policy; GitHub Actions provides the Bats validation.

[shunk031]

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark 'MacOS benchmark'.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.50.

Benchmark suite	Current: c4b0072	Previous: 4a5ae05	Ratio
zsh average startup time	0.154 Second	0.081 Second	1.90

This comment was automatically generated by workflow using github-action-benchmark.

CC: @shunk031