feat(caldav): add CalDAV integration for calendar CRUD

[penso]

Summary

• New moltis-caldav crate providing calendar CRUD operations (list calendars, list/create/update/delete events) via the CalDAV protocol using libdav and icalendar
• Supports Fastmail, iCloud, and generic CalDAV servers with multi-account configuration under [caldav.accounts.<name>]
• Feature-flagged as caldav, enabled by default in both gateway and CLI crates
• Lazy client initialisation on first use, ETag-based concurrency control for updates/deletes

Files changed

Area	Files
New crate	crates/caldav/ (client, discovery, ical, tool, types)
Config	schema.rs, validate.rs, lib.rs — CalDavConfig + schema map + semantic warnings
Wiring	gateway/Cargo.toml, cli/Cargo.toml, server.rs — feature flag + tool registration
Workspace	Root Cargo.toml + Cargo.lock — new deps (libdav, icalendar, hyper stack)
Changelog	CHANGELOG.md — Added entry

Validation

Completed

• taplo fmt — TOML files formatted
• cargo +nightly fmt --all — Rust code formatted
• cargo +nightly clippy --workspace --all-targets — 0 warnings
• cargo check --workspace — clean compilation
• cargo test -p moltis-caldav — 26 tests pass (types, ical, discovery, tool)
• cargo test -p moltis-config — 70 tests pass (schema drift guard covers new fields)

Remaining

• ./scripts/local-validate.sh — running post-PR creation
• Integration test with real CalDAV server (gated behind CALDAV_TEST_URL env var, not yet written)

Manual QA

None — no UI changes; tool is only accessible to the LLM agent via the tool registry.

[codspeed-hq]

Merging this PR will improve performance by ×2.7

⚡ 1 improved benchmark
✅ 33 untouched benchmarks
⏩ 1 skipped benchmark¹

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	session_store_list[10]	39 µs	14.6 µs	×2.7

---

_{Comparing caldav (117e65b) with main (45cbf7c)}

Footnotes

1. 1 benchmark was skipped, so the baseline result was used instead. If it was deleted from the codebase, click here and archive it to remove it from the performance reports. ↩

[codecov]

Codecov Report

❌ Patch coverage is 73.75415% with 237 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/caldav/src/tool.rs	61.31%	94 Missing ⚠️
crates/caldav/src/client.rs	0.00%	65 Missing ⚠️
crates/caldav/src/ical.rs	89.05%	22 Missing ⚠️
crates/gateway/src/server.rs	0.00%	17 Missing ⚠️
crates/config/src/validate.rs	63.88%	13 Missing ⚠️
crates/config/src/schema.rs	57.14%	9 Missing ⚠️
crates/gateway/src/auth_webauthn.rs	0.00%	6 Missing ⚠️
crates/agents/src/providers/github_copilot.rs	0.00%	5 Missing ⚠️
crates/caldav/src/discovery.rs	91.42%	3 Missing ⚠️
crates/gateway/src/state.rs	0.00%	3 Missing ⚠️

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