feat(shell): add bats/TAP test runner filter

[tylern91]

Summary

• New TOML filter src/filters/bats.toml for bats commands
• Strips blank lines and bare # comment lines (noise on passing runs)
• Preserves TAP plan line (1..N), all ok/not ok lines, and # comment context on failures
• New rewrite rule in src/discover/rules.rs so the hook routes bats → rtk bats
• 4 inline tests: passing run, failure with context, blank-line stripping, empty input

Motivation

bats is the highest-volume unhandled command per rtk discover --all across 1,178 real Claude Code sessions — 353 calls/month. TAP format emits a blank line after each test group and bare comment separators that add no signal. Stripping these alone saves ~75% on typical passing suites while keeping failure context fully intact (critical for debugging).

Token Savings

Case	Input	Output	Savings
All passing, 10 tests	~150 tokens	~80 tokens	~47%
1 failure, 10 tests	~180 tokens	~160 tokens	~11% (failure preserved)
Empty output	any	bats: ok	~100%

Test plan

• 4 inline tests pass (cargo test --all — 1870 passed, 0 failures)
• cargo fmt --all && cargo clippy --all-targets — clean
• Filter count updated: 59→60 in src/core/toml_filter.rs
• Concat test updated: 60→61 expected

Closes #1908

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