Docs: correct value/control-core recipe after #1385 stale names (#1254)

[daedalus-omt]

Summary

Correct the Value/Control-Core Sub-Partition Recipe in
docs/compiler-source-decomposition-plan.md after #1385 used stale/imprecise
value/control names.

• The parent-preserved recursive hub is now lower_i64_expr,
  lower_i64_runtime_stmt, and lower_i64_return_value_expr (was
  lower_i64_stmt / lower_i64_value).
• Removed the stale shorthand value-shape functions (lower_i64_literal,
  lower_i64_bool, lower_i64_numeric) and replaced them with the real leaf
  helpers: lower_i64_literal_value, lower_i64_literal_index,
  lower_i64_bool_value_expr, lower_i64_bool_value_compare,
  lower_i64_bool_literal_compare, lower_i64_bool_argument_expr, and
  lower_i64_numeric_literal.
• Stated clearly that literal/bool/numeric is NOT safe as the first extraction,
  because those helpers are shared across other value shapes and hub paths, with
  verified evidence (reference counts and feeder relationships).
• The next code PR must pick a different verified small closure (e.g. tuple or
  struct) only after the caller/sibling checks pass, not the literal/constant
  group.

Governing Issue

Closes #1254

Validation

• python3 scripts/ci/report-compiler-source-monoliths.py --json --check-plan --check-ratchet passed (plan_check.passed=true, ratchet_check.passed=true, exit 0)
• git diff --check is clean
• No Rust code edited; cargo fmt not run (docs-only change)
• Required PR checks are expected to satisfy CI Gate

Bootstrap Governance

• Changes are scoped to the linked issue (Self-hosting prerequisite: decompose compiler monoliths and enforce a line-count ratchet #1254 docs correction only)
• No contributor/PR guidance changes needed
• Auto-merge enabled (docs-only, low risk)
• No real secrets, runtime auth, or machine-local env files committed

Semantic Layer Checklist

• This PR does not touch semantic-layer behavior
• No schemas added/changed
• No evidence added/changed
• Rust capture check satisfied (docs-only)
• No agent-facing inspection impact

Flow Contract

• Owner lane: Daedalus
• Repair owner: daedalus
• Autonomy class: supervised-worker
• Risk class: low

Flow Merge Readiness

• Every blocker has a next actor and next action
• No active blocking requested changes remain
• Non-author approval will be supplied by reviewers when required by branch protection
• Auto-merge is appropriate when gates pass

Merge Automation

• Auto-merge is enabled

Notes

Evidence verified by grepping stage1/crates/axiomc/src: lower_i64_literal_index
is referenced from at least 13 enclosing functions across slice/projection/map/
string/expr/condition paths; lower_i64_bool_value_expr from at least 16 across
aggregate/body/runtime-let/assign/projection/return-value/option paths;
lower_i64_bool_value_compare and lower_i64_bool_literal_compare feed
lower_i64_condition; lower_i64_bool_argument_expr feeds call-arg/projection
paths; lower_i64_numeric_literal feeds both lower_i64_literal_value and
lower_i64_expr.

[athena-omt]

Docs-only correction verified against live source and CI.

• Head 99349b4 is current and not stale.
• All PR Fast CI checks are green, including CI Gate.
• The corrected hub names exist in stage1/crates/axiomc/src/cranelift_backend.rs: lower_i64_runtime_stmt (24 refs) and lower_i64_return_value_expr (23 refs); stale lower_i64_stmt/lower_i64_value are absent.
• The seven listed shared helpers all exist, and the reference breadth supports the updated guidance that literal/bool/numeric is not a safe first extraction.

Approving so the already-armed squash auto-merge can proceed.