fix(hook): prevent flag injection in rtk-rewrite hooks (#1350)

[ousamabenyounes]

Fixes #1350.

The Claude/Cursor rewrite hooks called rtk rewrite "$CMD" without a -- terminator. When a user command begins with a hyphen (--help, -h), clap interprets it as a flag to the rewrite subcommand: it prints help/usage text and exits 0. The hook then feeds that help text back to the agent as the "rewritten" command, which is shell-executed — a flag-injection footgun.

Fix

• Add the -- terminator: rtk rewrite -- "$CMD" in both hooks/claude/rtk-rewrite.sh and hooks/cursor/rtk-rewrite.sh, so hyphen-prefixed input is always captured as a positional arg.
• Add a clap-level regression test asserting rtk rewrite -- <flagish> parses the input as a positional rather than triggering clap's built-in help/version paths.
• Add hook-level shell tests (section 5b) covering --help, -h, --version, -V, and lone --.

Test verification (RED → GREEN)

RED - prod fix reverted (rtk rewrite "$CMD"), hooks/claude/test-rtk-rewrite.sh section 5b:

--- Flag injection safety (#1350) ---
  FAIL flag injection: --help must not trigger clap help
  -h, --help
  FAIL flag injection: -h must not trigger clap short help
  -h, --help           Print help (see more with '--help')

GREEN - with the -- terminator, after rebasing onto current develop:

--- Flag injection safety (#1350) ---
  PASS flag injection: --help must not trigger clap help -> (no rewrite)
  PASS flag injection: -h must not trigger clap short help -> (no rewrite)
  PASS flag injection: --version must not trigger clap version -> (no rewrite)
  PASS flag injection: -V must not trigger clap short version -> (no rewrite)
  PASS flag injection: lone -- must not crash the hook -> (no rewrite)

Rust targeted regression:

cargo test test_rewrite_clap_double_dash_blocks_flag_injection
test tests::test_rewrite_clap_double_dash_blocks_flag_injection ... ok
test result: ok. 1 passed; 0 failed

Full local gate after rebase:

cargo fmt --all --check && cargo clippy --all-targets && cargo test
test result: ok. 2393 passed; 0 failed; 8 ignored
test result: ok. 6 passed; 0 failed
test result: ok. 11 passed; 0 failed
test result: ok. 6 passed; 0 failed
test result: ok. 14 passed; 0 failed
test result: ok. 5 passed; 0 failed
test result: ok. 11 passed; 0 failed

(Re-proposes the work from the accidentally-closed #1370, rebased onto current develop.)

[ousamabenyounes]

Rebased this PR onto current develop and pushed 960dc37. The conflict is resolved, the PR is mergeable again, and the latest GitHub CI is green across fmt, clippy, tests on Ubuntu/Windows/macOS, security scans, benchmark, and CLA. Ping @aeppling

[pszymkowiak]

Reproduced the bug live, and re-tested with real usage after the fix — no regressions (git status, git log -10, cargo test --release, chained commands, ls -al all rewrite identically to before). Hook shell test suite passes 5/5 on the flag-injection cases. cargo fmt, cargo clippy --all-targets, cargo test --all all clean.