fix(registry): fi in IGNORED_PREFIXES shadows find commands

[hoklims]

Summary

• "fi" (shell keyword for ending if blocks) was listed as a bare string in IGNORED_PREFIXES
• "find".starts_with("fi") is true, so all find commands were classified as Ignored
• This meant rtk rewrite "find ..." always returned exit 1 (no rewrite), making the hook system unable to intercept find commands
• Same issue affected "done" which could shadow hypothetical commands starting with done

Fix

• Move "fi" and "done" from IGNORED_PREFIXES to IGNORED_EXACT (exact match only)
• Both copies of these constants in registry.rs are fixed
• Added 3 regression tests: find is now Supported, bare fi and done remain Ignored

Root cause analysis

IGNORED_PREFIXES check (line ~310):
  for prefix in IGNORED_PREFIXES {
      if trimmed.starts_with(prefix) {  // "find ...".starts_with("fi") == true!
          return Classification::Ignored;
      }
  }
  // Never reaches REGEX_SET matching for find commands

Other shell keywords like then, else, do already used the "keyword\n" / "keyword " suffix pattern to avoid this. fi and done were the only bare entries without a trailing delimiter.

Test plan

• cargo test — 416 passed, 0 failed
• rtk rewrite "find . -name foo" → rtk find . -name foo (was exit 1 before)
• rtk rewrite "git status" → rtk git status (no regression)
• rtk rewrite "ls -la" → rtk ls -la (no regression)

Partially fixes #170, #204, #236 — those issues reported find failures due to flag syntax mismatch, but the deeper blocker was that find was never classified as supported in the first place.

[Copilot]

Pull request overview

Fixes a command-classification bug in the discovery registry where shell keywords in the ignored prefix list caused unrelated commands (notably find) to be incorrectly classified as Ignored, preventing rewrite/hook interception.

Changes:

• Moves fi and done from IGNORED_PREFIXES (prefix match) to IGNORED_EXACT (exact match) to avoid shadowing commands like find.
• Adds regression tests ensuring find ... is classified as Supported while bare fi / done remain Ignored.

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[pszymkowiak]

Clean fix. Moving "fi" and "done" to IGNORED_EXACT is exactly right — the other shell keywords already used suffix delimiters ("do\n", "do ", "if ", etc.) to avoid this class of prefix
collision, fi and done were just missed.

Regression tests cover the important cases. LGTM.