feat: undo/redo system, action history, and LLM-agent CLI ergonomics

[e6qu]

Summary

• Undo/redo system: Linear timeline with cursor model. All mutating commands (init, mode, veil, unveil, apply, restore, checkpoint, gc, clean) record pre/post state snapshots to .funveil/history/log.yaml. Undo restores pre-state (config + files from CAS), redo restores post-state. New action after undo discards future. 500-entry cap with auto-truncation.
• Action history: fv history lists past/future actions with timestamps. fv history --show <id> shows config diffs and file size changes for a specific action.
• --json global flag: Machine-readable JSON output via CommandResult enum with #[serde(tag = "command")]. Errors include error codes (E001-E034). Enables LLM agents to parse fv output programmatically.
• --dry-run flag: Added to veil, unveil, and apply — previews what would change without modifying state.
• --files flag on status: Per-file state reporting (veiled/unveiled, full/partial, ranges).
• New commands: undo [--force], redo, history [--limit N] [--show <id>]

Files changed

File	Changes
src/history.rs	New — ActionRecord, ActionState, FileSnapshot, ActionHistory with 18 unit tests
src/main.rs	New commands, --json/--dry-run/--files flags, CommandResult enum, history integration, 15 new tests
src/error.rs	HistoryEmpty, NothingToRedo, ActionNotUndoable variants + code() method
src/config.rs	HISTORY_DIR constant, normalize_path() helper, history dir in ensure_data_dir()
src/lib.rs	Register history module, new re-exports
Cargo.toml	serde_json made unconditional dependency

Test plan

• cargo test --all-features — all 1,724 tests pass (33 new)
• cargo clippy --all-targets --all-features -- -D warnings — clean
• Manual: fv init → fv veil src/ → fv history → fv undo → verify restored → fv redo → verify veiled again
• Manual: fv veil src/ --json → valid JSON; fv veil src/ --dry-run → no state change
• Manual: fv status --files --json → per-file detail as JSON
• Manual: fv history show 2 → shows config diff and file size changes

[github-actions]

🔒 Security Report

Check	Status
cargo audit	✅ Pass
cargo deny	✅ Pass
pip-audit	✅ Pass

[github-actions]

Coverage Report

Metric	PR	Base	Delta
Statement	97.01%	97.36%	-0.36% (regression)
Branch	89.09%	89.43%	-0.33% (regression)

Per-file coverage (28 files)

File	Statement	Branch	Lines
/home/runner/work/funveil/funveil/src/update.rs	84.4%	83.3%	92/109
/home/runner/work/funveil/funveil/src/parser/languages/markdown.rs	91.4%	73.3%	85/93
/home/runner/work/funveil/funveil/src/output.rs	93.8%	100.0%	45/48
/home/runner/work/funveil/funveil/src/parser/languages/typescript.rs	93.8%	80.0%	285/304
/home/runner/work/funveil/funveil/src/main.rs	94.0%	84.4%	1402/1492
/home/runner/work/funveil/funveil/src/parser/languages/xml.rs	94.2%	71.4%	49/52
/home/runner/work/funveil/funveil/src/parser/languages/css.rs	94.4%	80.0%	102/108
/home/runner/work/funveil/funveil/src/veil.rs	95.0%	92.1%	627/660
/home/runner/work/funveil/funveil/src/logging.rs	95.2%	75.0%	60/63
/home/runner/work/funveil/funveil/src/history.rs	95.5%	91.7%	85/89
/home/runner/work/funveil/funveil/src/parser/languages/go.rs	97.2%	80.3%	310/319
/home/runner/work/funveil/funveil/src/parser/languages/html.rs	97.3%	61.5%	109/112
/home/runner/work/funveil/funveil/src/parser/languages/zig.rs	97.5%	82.8%	274/281
/home/runner/work/funveil/funveil/src/checkpoint.rs	97.9%	93.5%	235/240
/home/runner/work/funveil/funveil/src/cas.rs	98.5%	92.6%	128/130
/home/runner/work/funveil/funveil/src/analysis/call_graph.rs	99.0%	82.5%	283/286
/home/runner/work/funveil/funveil/src/patch/manager.rs	99.1%	83.3%	347/350
/home/runner/work/funveil/funveil/src/patch/parser.rs	99.3%	93.6%	268/270
/home/runner/work/funveil/funveil/src/analysis/cache.rs	99.4%	94.4%	163/164
/home/runner/work/funveil/funveil/src/parser/tree_sitter_parser.rs	99.5%	93.8%	611/614
/home/runner/work/funveil/funveil/src/types.rs	99.6%	97.0%	272/273
/home/runner/work/funveil/funveil/src/analysis/entrypoints.rs	100.0%	97.3%	754/754
/home/runner/work/funveil/funveil/src/config.rs	100.0%	100.0%	295/295
/home/runner/work/funveil/funveil/src/error.rs	100.0%	0.0%	37/37
/home/runner/work/funveil/funveil/src/parser/mod.rs	100.0%	100.0%	167/167
/home/runner/work/funveil/funveil/src/perms.rs	100.0%	100.0%	35/35
/home/runner/work/funveil/funveil/src/strategies/header.rs	100.0%	94.4%	151/151
/home/runner/work/funveil/funveil/src/strategies/mod.rs	100.0%	0.0%	17/17