Implement compatible optimization, debug, and tail-call modes

Parent: #8
Blocked by: #35 and #36

Outcome

Build an explicit deterministic optimization pipeline that honors the existing compiler-mode contract.

Acceptance criteria

• Identity, debug, release, optimization, tail-call, and related mode decisions are explicit and traced.
• Passes preserve source and debug anchors as required and never apply aggressive optimization unconditionally.
• Optimized and unoptimized outputs pass differential runtime, API, exception, debugging, and NativeAOT checks.
• Tail calls, inlining, closure and state-machine transformations, constant and dead-code simplification, and other passes are enabled only for their compatible modes.
• Pass ordering is deterministic and invalidation fingerprints include every semantic optimization input.
• New optimizations require correctness evidence plus compile-time and generated-code benchmarks; benchmark-justified kernels follow ADR 0007.
• Slow compiler work contributes phase and critical-path data to the structured trace required by ADR 0016.

Decision inputs

Issues #3, #5, and #12; ADRs 0007, 0015, 0016, and 0017.

This issue inherits the corpus-neutral acceptance policy in #8.

Start with parent issue #8 and the blocking issues #35 and #36, then read decision inputs #3, #5, #12 and ADRs 0007, 0015, 0016, and 0017. The work is done when the listed mode, compatibility, determinism, correctness, benchmarking, and tracing acceptance criteria are satisfied across the required checks.