docs(user): de-dev polish — strip internal scaffolding from user docs (Phase 3a) (#226)

Remove developer-only scaffolding that leaked into the public user/operator
docs, while preserving every user-facing behavior, command, flag, endpoint,
constant, and env var. No behavior changes.

Removed across 18 files:
- internal ticket / sequencing refs (MR-NNN, RFC-NNN, "Phase N");
- source-code paths (crates/**/*.rs, *.pest) and internal struct/function
  dumps (e.g. the QueryIR / GraphCommit / SchemaMigrationPlan Rust types,
  internal fn names like fork_branch_from_state, optimize_all_tables);
- Lance-internal blocker prose (upstream issue numbers, blob-decode cause,
  sidecar Phase-B/C mechanics) — keeping the user-visible behavior (e.g.
  "optimize skips Blob-column tables; reads/writes unaffected");
- pre-v0.4.0 Run-state-machine archaeology.

Internal IR/lowering/recovery-internals sections were either trimmed to a
brief user-facing note (e.g. "Traversal execution", "interrupted writes
recover automatically; recovery commits are recorded under actor
omnigraph:recovery") or removed.

Kept: all language syntax, lint codes, Cedar actions/scopes, endpoints,
error taxonomy, every constant and env var (verified none dropped from the
constants cheat-sheet), and the operator-facing explanations of on-disk
artifacts. Residual "legacy" mentions are all user-facing (the deprecated
omnigraph.yaml, the legacy token chain, old command names).

Verified: zero internal-scaffolding leaks (MR/RFC/Phase/.rs/.pest = 0) across
docs/user; zero broken links; check-agents-md.sh green.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

docs/user/queries/index.md

@@ -1,7 +1,5 @@
 # Query Language (`.gq`)
 
-Pest grammar at `crates/omnigraph-compiler/src/query/query.pest`. AST in `query/ast.rs`. Type checker in `query/typecheck.rs`. Lowering in `ir/lower.rs`.
-
 ## Query declarations
 
 ```
@@ -49,40 +47,19 @@ Param types reuse all schema scalars; trailing `?` makes a param optional. The c
 Write statements (`insert` / `update` / `delete`) are documented on the
 [mutations](../mutations/index.md) page.
 
-## IR (Intermediate Representation)
+## Traversal execution
 
-`QueryIR { name, params, pipeline: Vec<IROp>, return_exprs, order_by, limit }`
+Variable-length traversals (`Expand`) are executed one of two ways, chosen per-expand by a cost model over cheap manifest counts (frontier size, edge count, source-vertex count, hops) plus index coverage: selective traversals (small frontier relative to the source set) resolve neighbors from the persisted `src`/`dst` BTREE (one indexed scan per hop); dense / deep / large-frontier traversals — or those whose BTREE coverage is degraded so a full scan would be paid per hop — use an in-memory CSR adjacency index. Both produce identical results. The `OMNIGRAPH_EXPAND_INDEXED_MAX_FRONTIER` / `OMNIGRAPH_EXPAND_INDEXED_MAX_HOPS` ceilings bound the *initial dispatch* frontier/hops (beyond them CSR is always used); the cost model estimates total indexed work as ~`hops × frontier × fanout` and prices dense fan-out toward CSR — they are not a hard per-hop bound. `OMNIGRAPH_TRAVERSAL_MODE=indexed|csr` forces a mode (see [constants](../reference/constants.md)).
 
-Pipeline operations:
-
-- `NodeScan { variable, type_name, filters }`
-- `Expand { src_var, dst_var, edge_type, direction (Out|In), dst_type, min_hops, max_hops, dst_filters }` — destination filters are pushed *into* the expand so Lance scalar pushdown can prune. Executed one of two ways, chosen per-expand by a cost model over cheap manifest counts (frontier size, |E|, source-vertex count, hops) plus index coverage: selective traversals (small frontier relative to the source set) resolve neighbors from the persisted `src`/`dst` BTREE (one indexed scan per hop); dense / deep / large-frontier traversals — or those whose BTREE coverage is degraded so a full scan would be paid per hop — use the in-memory CSR adjacency index. Both produce identical results. The `OMNIGRAPH_EXPAND_INDEXED_MAX_FRONTIER` / `OMNIGRAPH_EXPAND_INDEXED_MAX_HOPS` ceilings bound the *initial dispatch* frontier/hops (beyond them CSR is always used); the cost model estimates total indexed work as ~`hops × frontier × fanout` and prices dense fan-out toward CSR — they are not a hard per-hop bound. `OMNIGRAPH_TRAVERSAL_MODE=indexed|csr` forces a mode (see [constants](../reference/constants.md)).
-- `Filter { left, op, right }`
-- `AntiJoin { outer_var, inner: Vec<IROp> }` — for `not { … }`
-
-Lowering:
-
-1. Partition MATCH clauses (bindings, traversals, filters, negations).
-2. Identify "deferred" bindings (a destination of a traversal that has filters) so the Expand can carry the filter as a pushdown.
-3. Emit NodeScan for the first binding, then Expand operations, then remaining Filter operations, then AntiJoins for negations.
-4. Translate RETURN / ORDER expressions; preserve LIMIT.
-
-## Linting & validation (`query/lint.rs`)
+## Linting & validation
 
 Codes seen so far:
 
 - **Q000** (Error): parse error
 - **L201** (Warning): nullable property never set by any UPDATE — "{type}.{prop} exists in schema but no update query sets it"
 - (Warning): mutation declares no params — hardcoded mutations are easy to miss
-- Plus all type errors from `typecheck_query_decl()` (undefined types, mismatched operators, undefined edges, etc.)
+- Plus all type errors from type checking (undefined types, mismatched operators, undefined edges, etc.)
 
-Output:
-
-```
-QueryLintOutput { status, schema_source, query_path,
-  queries_processed, errors, warnings, infos,
-  results: [{ name, kind, status, error?, warnings[] }],
-  findings: [{ severity, code, message, type_name?, property?, query_names[] }] }
-```
+Lint output reports an overall status, per-query results (name, kind, status, any error and warnings), and structured findings (severity, code, message, and the type/property/query they apply to).
 
 CLI exits non-zero only on `status = Error`.