api: CompiledRegex should carry its MatchMode to prevent silent misuse

Problem

CompiledRegex stores only nfa : GlushkovNfa with no record of the MatchMode used during compilation. Both matchCompiled and searchCompiled call the identical Glushkov.matchString underneath — the mode distinction is only enforced inside desugar (which wraps unanchored patterns with .* in search mode).

This means a caller who compiles with .search and then calls matchCompiled instead of searchCompiled silently gets wrong semantics — no error, no warning.

-- Silent misuse: compiled for search, used as fullMatch
let compiled ← compile pattern .search
let result := matchCompiled compiled input  -- wrong! should be searchCompiled

Proposed fix

Add a mode : MatchMode field to CompiledRegex and assert (or dispatch) on it in matchCompiled/searchCompiled:

structure CompiledRegex where
  nfa  : Glushkov.GlushkovNfa
  mode : MatchMode
deriving Repr

Option A: panic/error if wrong function called for mode.
Option B: merge into a single runCompiled that dispatches based on stored mode.
Option C: remove matchCompiled/searchCompiled and expose only runCompiled.

Option C (single entry point) is cleanest — callers can't pick the wrong function.

Impact

Breaking API change for matchCompiled/searchCompiled. The CLI (LckGrep.lean) and tests need updating.

Empieza localizando CompiledRegex, compile, matchCompiled, searchCompiled y desugar; después, inspecciona el punto de entrada de la CLI en LckGrep.lean y las pruebas afectadas. Decide qué forma de API propuesta es la prevista, actualiza los llamadores y las pruebas, y verifica que los modos de coincidencia incompatibles ya no puedan usarse silenciosamente.