fix(37-12): narrator re-declares confrontation on scene transitions

[slabgorb]

Summary

• Adds a === TRANSITION CONFRONTATION === section to the narrator prompt whenever an encounter is active, telling the narrator it may re-emit the confrontation field when the scene shifts to a different type. Lists every OTHER confrontation type from the genre pack as a concrete target (current type filtered out — Case C redeclare is a no-op).
• Removes the contradictory "Only emit confrontation on the turn the encounter STARTS" instruction from the is_none() branch. 37-13 built the encounter gate to route re-emits across Cases C/D/E; the prompt was actively telling the narrator not to send them.
• Emits encounter.transition_guidance_injected (StateTransition type) with current_encounter_type and alternative_count fields so the GM panel can verify the narrator was shown N transition options on every turn with an active encounter.

Scope: prompt-string edit in build_prompt_context + one WatcherEventBuilder::send(). No new types, no new public API, no subsystem boundary changes. The block sits outside the inner find_confrontation_def() guard on purpose so a broken-def encounter can still receive a recovery menu — the existing ValidationWarning independently signals the broken state.

Efficiency: the TEA verify phase applied one simplify fix (replaced a Vec<&ConfrontationDef> collect+iterate with a direct filter+counter loop). Review phase applied four nits: code comment honesty (name all six gate cases explicitly), test bounded window via === END TRANSITION CONFRONTATION ===, narrowed phrase test to canonical re-emit, and a test docstring fix for a six-cases/five-names contradiction.

Test plan

• 7/7 Story 37-12 source-scan integration tests pass (narrator_confrontation_redef_story_37_12_tests)
• 419/419 sidequest-server integration suite green — zero regressions
• cargo clippy -p sidequest-server --tests -- -D warnings clean
• cargo fmt clean
• Playtest verification: on next playtest, watch the GM panel's encounter filter for encounter.transition_guidance_injected events to confirm the block is actually reached at runtime. Source-scan tests prove the code is present and textually correct; only runtime observation proves the turn-loop exercises it.

Known follow-ups (not blocking)

• encounter_gate.rs:10-12 doc comment incorrectly claims 37-13 is the "root cause fix" for 37-12 — should be softened to "dispatch-side prerequisite". Risk: a future agent dismisses related work as already-shipped.
• prompt.rs:362 AVAILABLE CONFRONTATIONS block runs unconditionally; mid-encounter the narrator now sees both that list and the new TRANSITION CONFRONTATION list. Pre-existing design, not introduced by this PR.
• Field format format!("- \"{}\" ...", alt.confrontation_type, ...) doesn't escape YAML-sourced quotes/newlines. Pre-existing at prompt.rs:372. Appropriate fix is validation at ConfrontationDef deserialization time.

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