fix(explore): improve query accuracy for file paths, camelCase, and variables

`codegraph_explore` previously struggled with accurately interpreting user queries. Explicitly named file paths were shredded, making it hard to target specific files; natural language queries often missed camelCase identifiers; and state held in variables was overlooked as starting symbols.

This commit introduces several improvements:
- **Reliable File Path Resolution:** Naming a file by its path in a `codegraph_explore` query now works reliably. The path is resolved against the index, and that file is guaranteed a place at the top of the answer. Previously, paths were broken into fragments — bracketed route segments like SvelteKit's `[id]` made this worst — and pieces like `page` or `runs` matched every sibling file, so the file you actually named could be crowded out. A path that doesn't match any indexed file is now called out instead of silently ignored.
- **CamelCase Matching for Queries:** Plainly-worded `codegraph_explore` questions now find camelCase code. A query like "auto-scroll to bottom" can reach a function named `scrollFeedToBottom`, because query words are matched against the words inside identifiers, not just whole names.
- **Variable and Constant Seeding:** Variables and constants now count when `codegraph_explore` picks its starting symbols, so state held in plain variables — `$state`-style variables in Svelte, for example — no longer gets overlooked.

CHANGELOG.md

@@ -21,6 +21,9 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### Fixes
 
+- Naming a file by its path in a `codegraph_explore` query now works reliably: the path is resolved against the index and that file is guaranteed a place at the top of the answer. Previously the path was broken into fragments — bracketed route segments like SvelteKit's `[id]` made this worst — and pieces like `page` or `runs` matched every sibling file, so the file you actually named could be crowded out of the answer entirely. A path that doesn't match any indexed file is now called out instead of silently ignored.
+- Plainly-worded `codegraph_explore` questions now find camelCase code: a query like "auto-scroll to bottom" can reach a function named `scrollFeedToBottom`, because query words are matched against the words inside identifiers, not just whole names.
+- Variables and constants now count when `codegraph_explore` picks its starting symbols, so state held in plain variables — `$state`-style variables in Svelte, for example — no longer gets overlooked.
 - C, C++, Objective-C and Rust unions are now indexed as first-class `union` nodes. A `union` declaration previously produced no symbol at all, so it never appeared in search or `codegraph_explore`, and anything attached to it disappeared with it — in Rust, every `impl SomeTrait for MyUnion` lost its edge, the methods from that impl were left pointing at a type the graph did not contain, and asking which types implement a trait quietly skipped the union ones. A union-shaped dispatch table in C now resolves its function pointers like a struct-shaped one. A `typedef union { … } Name;` in C keeps the typedef's name and is no longer mistaken for a plain type alias. Thanks @ctype-lab. Re-index after upgrading to pick up unions in existing projects. (#1515)
 
 - A long-lived index no longer drifts away from what a fresh `codegraph index` would produce. When a file gained or lost a symbol, references to that name in files the sync never touched kept pointing at the definition that was correct before the change, and — because nothing distinguished two same-named definitions — the winner could come down to the order files happened to be written, which differs between a full index and a sync. On this project's own repository, replaying 80 commits through `sync` left 5.7% of connections wrong; it is now 1.3%, and the wrong-answers-still-being-asserted half drops by 99.7%. Since call edges are what flow questions follow and what `codegraph_explore` ranks files by, this quietly degraded answers as an index aged, with nothing to indicate it. Syncing is unchanged in speed, and an edit that only changes a function's body does no extra work at all. Set `CODEGRAPH_NO_REBIND=1` to opt out.