feat(refacto-p3): quoted env prefix + inline regex cleanup + routing docs

[aeppling]

Summary

• ENV_PREFIX now handles FOO="bar baz", FOO='val', escaped quotes
• Move 6 inline lazy_static regex to module level
• Merge rewrite_head_numeric + rewrite_tail_lines → rewrite_line_range
• Consolidate head/tail call sites in rewrite_segment
• Add rewrite pipeline documentation to TECHNICAL.md
• Rewrite discover README as concept/flow documentation
• Add lexer-based tokenizer for shell command parsing

Test plan

• cargo fmt --all && cargo clippy --all-targets && cargo test — 1219 passed, 1 pre-existing dotnet skip (WSL2 timestamp granularity)
• Release binary build: cargo build --release
• 30 real-world rewrite tests: basic commands (git status, cargo test, gh pr view, pnpm list, docker ps, kubectl get, curl, ls, grep, find)
• 25 complex compound commands: chained &&/||/;, pipes with grep/head/tail, redirects 2>&1/>/dev/null, quoted operators inside strings (git commit -m "fix
  && update")
• 10 ENV_PREFIX edge cases: FOO="bar baz" git status, FOO='val' git status, A="x y" B=1 sudo git status, FOO="he said "hello"" git status,
  RTK_DISABLED=1 git status, POSIX 'it'''s' (correctly rejected as 3 tokens)
• Head/tail rewrites: head -20 file, head --lines=10 file, tail -5 file, tail -n 10 file, tail --lines=20 file, tail --lines 15 file — all produce correct
  rtk read output
• Guard checks: cat file > out (skip — write op), gh pr list --json (skip — structured output), find . -name "*.rs" | xargs grep (skip — pipe consumer)
• All 12 existing head/tail/cat snapshot tests unchanged