feat(mir): close canonical callable identity boundary

[sanohiro]

Summary

• replace backend stringly callable dispatch with typed program/runtime identities
• encode program symbols and assign deterministic canonical identities to generated function-value, closure, task, and parallel kernels
• add canonical type/function ABI graph codecs, fail-closed validation, collision preflight, and exported/per-unit/ThinLTO identity coverage
• close the review findings for legacy symbol owners, inline by-value recursion, and malformed ABI error precedence

Review

• one full-diff host-native review of d034eda9 reported three P2 findings
• all findings and their same-root owner/platform-lint failures are closed in 781d3528
• no public-contract, IR-shape, or cross-layer redesign was needed after review

Verification

• final-SHA focused owners: link hygiene, main ABI, parallel lowering, per-unit surface, and ThinLTO (82 passed)
• native pointer-conversion owners: DNS, TCP, UDP, process, and command runtime paths (39 passed)
• scripts/test-pr.sh
• scripts/cargo.sh clippy --workspace --lib --bins
• the local macOS preflight was INCOMPLETE at _dyld_start; isolated Linux ARM64 scripts/pre-pr.sh recorded the final-SHA attestation