Move derived loop facts into structured checking

[hiroki23]

Summary

• derive the accepted literal-zero and active base + small nonnegative literal
  loop facts while the structured checker consumes declarations, control flow,
  and assignments
• retain only the verified result or an enclosing verified-fact dependency in
  mir_loop_facts before QBE emission
• delete the lexical whole-loop proof scan, emitter-only local state 3, and
  the now-unused emitter function_end field
• extend negative controls for dynamic, negative, non-adjacent, and invalidated
  outer-loop derived facts

The QBE adapter now receives both accepted induction shapes through the same
checked-program fact boundary. Nested facts follow an already-derived enclosing
fact instead of rescanning token ranges, and the adapter never reconstructs a
derived initializer from source tokens.

Scope

This is the bounded ownership migration registered in #204. It does not add
general range propagation, dominance, interprocedural analysis, a serialized
MIR field, a backend option, or language/runtime behavior. The active-loop
emitted-value carrier and direct base-plus-literal expression propagation remain
temporary until the next general Native MIR control/value slice replaces them.

Verification

• trb fmt --check compiler/gate4/src/compiler.trb compiler/gate4/src/compiler_test.trb
• trb check --config compiler/gate4/trbconfig.jsonc
• TYPE_RB_NATIVE_ROOT="$PWD" trb test: 80/80
• trb test --config compiler/gate4/trbconfig.jsonc: 62/62
• eight positive/control application fixtures have byte-identical baseline and
  candidate QBE: literal-zero, derived, reassigned, non-unit, dynamic,
  negative, non-adjacent, and conditional
• an outer loop invalidated after checking a nested derived loop invalidates
  that dependency; the generated path retains negative-index normalization and
  an executable negative-index probe prints 40
• three local Darwin arm64 Native generations are 299,648 bytes each and emit
  byte-identical compiler QBE; the local linker varied only the Mach-O UUID and
  signature, so hosted exact executable identity remains authoritative
• the local fixed compiler QBE is 956,214 bytes with SHA-256
  f90ecf48bfb7a95a03b645130a6891de5b75b7af8ebfc0240996530821481bbd
• static target run
  passes at 299,656 Darwin bytes, 271,928 Linux bytes, and 571,584 bytes
  combined; target-neutral QBE is 956,214 bytes with the same SHA-256 recorded
  locally
• persistent-worker run
  passes at 299,696 and 271,920 stripped compiler bytes, 571,616 combined,
  while preserving the lifecycle and memory evidence
• Gate 6N run
  passes the current amd64 and arm64 regressions and cross-target contract
• complete Native gate
  passes every repository, runtime, benchmark, closure, and Go-free bootstrap
  check on exact head 0fdc4b6ebfe71f7135cbaa2a5caab6626dc90bdc

Closes #204