feat(picker): Unify readable labels and backend-native highlights

[mhiro2]

Summary

• Unify picker labels across backends into a readable format (symbol - path:line:col, or path:line:col
  when symbol is empty).
• Improve visual consistency by using backend-native highlight groups for candidate rendering in snacks and
  telescope.
• Reduced noise in documentSymbol candidates by preferring symbol names over verbose signatures.

Changes

• f8ec003 : refactor(picker): add unified readable label builder
  • Added shared label payload generation (label, symbol, path, display_lnum, display_col) for
    external pickers.
  • Hardened text normalization and added utility tests for label/path behavior.
• f1451bc : fix(snacks): improve readable labels and highlights
  • Reworked snacks item formatting into structured chunks for clearer symbol/path/line rendering.
  • Kept preview/jump behavior intact via preserved file/position metadata.
• 8b596e9 : fix(telescope): improve readable labels and highlights
  • Added chunk-based display rendering for telescope entries with readable symbol-first output.
  • Kept sorter/preview metadata behavior unchanged while improving visual clarity.
• ce42ce2 : fix(fzf-lua): separate visible label from location payload
  • Separated visible label text from selection payload to keep candidate lines readable.
  • Retained deterministic selection through index-based resolution for label collisions.
• 8b11cdc : fix(lsp): prefer symbol names over long detail text
  • Updated document symbol mapping to prioritize concise symbol names over verbose detail strings.
  • Reduced picker noise for long function/type signatures.
• 6de5142 : docs(picker): document unified readable labels
  • Documented the unified picker label format and expected backend behavior.
  • Synced README/help text with the new display policy.
• f3c290e : refactor(picker): deduplicate path chunk formatting
  • Extracted duplicated path chunk splitting into shared picker utility.
  • Removed backend-local duplication while preserving backend-specific highlight mapping.