feat(routines): add capability-rooted declaration source reader

[jscott3201]

Summary

• add a capability-relative adapter that reads the unique source identities in a declaration-requirement projection
• select release and development roots without fallback, preserve full identity and opaque bytes, and return documents in deterministic order
• enforce inclusive document, per-file, and total-byte limits before unbounded allocation
• hold opened file handles through metadata preflight and bounded reads, rejecting root escape, non-regular entries, growth, and inconsistent sizes atomically
• add cap-std 4.0.2 for confined relative filesystem access

Scope

Callers remain responsible for opening and validating checkout roots. The reader does not run Git, inspect pins or inventory, authenticate checkout identity, hash bytes, decode UTF-8, parse Modelica, or inspect declarations. Existing syntax checking remains the sole blob and content authority. No pipeline/CLI integration, production artifacts, schema changes, or external repository work is included.

Validation

• cargo fmt --manifest-path tools/routine-compiler/Cargo.toml -- --check
• focused declaration-source tests (14 passed)
• cargo test --locked --manifest-path tools/routine-compiler/Cargo.toml (109 passed)
• cargo clippy --locked --manifest-path tools/routine-compiler/Cargo.toml --all-targets -- -D warnings
• macOS capability tests, including external symlink escape rejection
• full Python lint suite (189 passed) and production lints
• G36 source inventory (431 release / 693 development files)
• G36 declaration, routine, verifier, and full scenario gates
• dataset harness (32 passed) and replay assertions
• generated book build

[jscott3201]

Cycle 1 consolidated review: PASS at 92407abb771feaf6484fa6df3144a02f117f3d09.

Both independent reviewers were blocker/major-clean. Deferred minor M1: full-identity deduplication uses bounded linear-vector membership, which can become quadratic at unusually high caller-selected document limits; current G36 scale and explicit limits make this non-blocking, so no code change is warranted in this PR.

Exact-head build and verify checks are green.