store: remove dead code and move params to config

Remove:
- score_weight() - never called
- position field on Node - never read (was for export)
- Provenance enum - inline helper for capnp migration
- migrate_transcript_progress + CLI command
- init_from_markdown, import_file, ingest_units
- export command and export_to_markdown
- RetrievalEvent, GapRecord types
- classify_filename, new_transcript_segment

Move spreading activation params to Config:
- default_node_weight, edge_decay, max_hops, min_activation
- Remove Params struct and StoreView::params()

Simplify cmd_init to just seed identity via upsert().
Simplify cmd_import to use parse_units + upsert directly.

-576 lines

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/hippocampus/store/ops.rs

@@ -268,22 +268,6 @@ impl Store {
         Ok((old, weight))
     }
 
-    /// Update a node's weight with a new score and record the scoring
-    /// timestamp. Uses asymmetric smoothing: responds quickly to high
-    /// scores (alpha=0.5) but decays slowly on low scores (alpha=0.1).
-    /// This keeps memories surfaced even if they're only useful 1 in 4 times.
-    /// Returns (old_weight, new_weight).
-    pub fn score_weight(&mut self, key: &str, score: f64) -> Result<(f32, f32)> {
-        let node = self.nodes.get_mut(key)
-            .ok_or_else(|| anyhow!("node not found: {}", key))?;
-        let old = node.weight;
-        let alpha = if score > old as f64 { 0.5 } else { 0.1 };
-        let new = (alpha * score + (1.0 - alpha) * old as f64) as f32;
-        node.weight = new.clamp(0.01, 1.0);
-        node.last_scored = chrono::Utc::now().timestamp();
-        Ok((old, node.weight))
-    }
-
     /// Set the strength of a link between two nodes. Deduplicates if
     /// multiple links exist. Returns the old strength, or error if no link.
     pub fn set_link_strength(&mut self, source: &str, target: &str, strength: f32) -> Result<f32> {