digest: split into focused modules, externalize prompts

digest.rs was 2328 lines containing 6 distinct subsystems. Split into:
- llm.rs: shared LLM utilities (call_sonnet, parse_json_response, semantic_keys)
- audit.rs: link quality audit with parallel Sonnet batching
- enrich.rs: journal enrichment + experience mining
- consolidate.rs: consolidation pipeline + apply

Externalized all inline prompts to prompts/*.md templates using
neuro::load_prompt with {{PLACEHOLDER}} syntax:
- daily-digest.md, weekly-digest.md, monthly-digest.md
- experience.md, journal-enrich.md, consolidation.md

digest.rs retains temporal digest generation (daily/weekly/monthly/auto)
and date helpers. ~940 lines, down from 2328.

Co-Authored-By: Kent Overstreet <kent.overstreet@linux.dev>

prompts/consolidation.md

@@ -0,0 +1,29 @@
+# Consolidation Action Extraction
+
+You are converting consolidation analysis reports into structured actions.
+
+Read the reports below and extract CONCRETE, EXECUTABLE actions.
+Output ONLY a JSON array. Each action is an object with these fields:
+
+For adding cross-links:
+  {"action": "link", "source": "file.md#section", "target": "file.md#section", "reason": "brief explanation"}
+
+For categorizing nodes:
+  {"action": "categorize", "key": "file.md#section", "category": "core|tech|obs|task", "reason": "brief"}
+
+For things that need manual attention (splitting files, creating new files, editing content):
+  {"action": "manual", "priority": "high|medium|low", "description": "what needs to be done"}
+
+Rules:
+- Only output actions that are safe and reversible
+- Links are the primary action — focus on those
+- Use exact file names and section slugs from the reports
+- For categorize: core=identity/relationship, tech=bcachefs/code, obs=experience, task=work item
+- For manual items: include enough detail that someone can act on them
+- Output 20-40 actions, prioritized by impact
+- DO NOT include actions for things that are merely suggestions or speculation
+- Focus on HIGH CONFIDENCE items from the reports
+
+{{REPORTS}}
+
+Output ONLY the JSON array, no markdown fences, no explanation.