feat: pnpm workspace filter support (--filter/-F)

Problem

Monorepo Node.js users (pnpm workspaces) get zero token savings from RTK because all their commands go through pnpm --filter <workspace> <tool>:

pnpm --filter web prettier --check .
pnpm --filter web tsc --noEmit
pnpm -F @scope/pkg vitest run

The rewrite layer and Clap parsing both fail to match these patterns. Root cause: every PATTERN regex assumes pnpm <subcommand> with no flags between pnpm and the subcommand. pnpm --filter web breaks all matching.

Strategy: Rewrite-Layer Normalization

Strip pnpm (--filter|-F) <workspace> in the rewrite layer before classification, then propagate the workspace value to tool modules via a hidden --pnpm-filter Clap global arg.

Why not pattern expansion: Adding pnpm --filter \S+ <tool> variants to every PATTERN regex and rewrite_prefixes array is combinatorial (7+ tools × 2 flag forms). Doesn't scale.

Expected behavior

# Hook rewrites transparently
pnpm --filter web prettier --check .  →  rtk prettier --pnpm-filter web --check .
pnpm -F web tsc --noEmit              →  rtk tsc --pnpm-filter web --noEmit
pnpm --filter web vitest run          →  rtk vitest --pnpm-filter web run
pnpm --filter web list                →  rtk pnpm --pnpm-filter web list

# rtk discover correctly classifies these as Supported (not Unsupported)
rtk discover  →  pnpm --filter web prettier  [Supported, ~70% savings]

Files to modify (10 total)

File	Change
src/discover/registry.rs	Rewrite core extraction, pnpm filter strip/inject, classify_command update
src/main.rs	--pnpm-filter global Clap arg + 8 dispatch updates
src/utils.rs	New package_manager_filtered_exec()
src/prettier_cmd.rs	Add pnpm_filter param
src/format_cmd.rs	Add pnpm_filter param
src/tsc_cmd.rs	Add pnpm_filter param
src/vitest_cmd.rs	Add pnpm_filter param
src/lint_cmd.rs	Add pnpm_filter param
src/playwright_cmd.rs	Add pnpm_filter param
src/pnpm_cmd.rs	Add pnpm_filter param

Edge cases

• Scoped packages: @scope/pkg — \S+ regex handles it
• Glob patterns: ./packages/* — \S+ handles it
• No filter: all existing behavior unchanged (pnpm_filter = None throughout)
• Env prefixes: sudo pnpm --filter web prettier — env prefix stripped first, re-added after rewrite
• Unknown commands: pnpm --filter web unknown-cmd → no rewrite (passthrough)

Out of scope (future)

• pnpm -w (workspace root flag)
• pnpm -r / --recursive
• pnpm --filter-prod

Related

Reported by Stephane (monorepo Node user via Slack).

Sub-issues: Phase 1 (#registry), Phase 2 (#main), Phase 3 (#utils), Phase 4 (#tool-modules)