feat(lpp): add entry-based project loading

[e54-bot]

Summary

• add the additive LPP 1.1 entry and projectLoading contract for provider-owned project loading
• update the mock provider and conformance runner to load isolated filesystem projects and preserve canonical source identities
• add success, failure, capability, invalid-parameter, and canonical-entry fixtures while preserving LPP 1.0 fixtures

Verification

• cargo fmt --all -- --check
• cargo clippy --all-targets -- -D warnings
• cargo test --workspace
• cargo build --release --locked --bin lpp-mock-provider --bin lpp-conformance-runner
• conformance validate/replay: 40 passed, 0 failed
• independent ablation: removing entry handling caused the project-loading scenario to fail

Fixes #16

[Teakowa]

Major — conformance/mock-provider/src/main.rs, documents_for_request: entry-based check/compile rejects any request containing projectRoot, but the normative common-parameter contract still defines projectRoot as OPTIONAL for check/compile and says providers MUST accept it. A conforming LPP 1.1 client can therefore be rejected with -32602. Accept/ignore projectRoot for entry requests (and cover that legal shape), or otherwise make the normative contract unambiguously exclude it.

Minor — spec/lpp-v1.md quick-reference table lists entry check/compile as requiring check or projectLoading / compile or projectLoading, while the actual negotiated behavior requires the method capability plus projectLoading. Change the table to express both requirements so third-party implementations do not treat projectLoading as a substitute for check or compile.

[Teakowa]

LGTM