docs: rename runs.md/runs.rs → writes and repoint all references (#131)

The Run state machine was removed in MR-771 (v0.4.0); `docs/dev/runs.md`
and `crates/omnigraph/tests/runs.rs` have since documented and tested the
direct-publish write path, so the "runs" name was misleading.

- git mv docs/dev/runs.md → docs/dev/writes.md (reframe H1 + intro;
  keep MR-771 history note)
- git mv crates/omnigraph/tests/runs.rs → tests/writes.rs (reframe header)
- repoint every runs.md / runs.rs reference across docs, AGENTS.md, and
  source comments
- fix four pre-existing broken `docs/runs.md` links (the file never lived
  at that path) to `docs/dev/writes.md`
- fix the stale v0.4.0 anchor to the live section

No behavior change: every source edit is a comment. Engine builds and the
renamed test passes 25/25; scripts/check-agents-md.sh passes.

The run-removal cleanup itself (run_registry.rs guard, __run__ prefix) is
deferred to MR-770.

docs/releases/v0.4.0.md

@@ -65,7 +65,7 @@ manifest. The next mutation against that table fails with
 `ExpectedVersionMismatch`. Most validation runs before any Lance write,
 so single-statement mutations are unaffected; the narrow path is
 multi-statement queries with late-op failures. Tracked as a follow-up;
-see [docs/dev/runs.md](../dev/runs.md#known-limitation-mid-query-partial-failure-on-the-same-table)
+see [docs/dev/writes.md](../dev/writes.md#mid-query-partial-failure-closed-by-mr-794)
 for the workaround.
 
 ## Upgrade notes

docs/releases/v0.4.1.md

@@ -19,7 +19,7 @@ mutation proceeds normally.
   HEAD on every staged table is untouched and the next mutation
   proceeds normally. A narrowed residual remains at the
   finalize→publisher boundary (multi-table `commit_staged` is not
-  atomic with the manifest commit) — see [docs/dev/runs.md](../dev/runs.md)
+  atomic with the manifest commit) — see [docs/dev/writes.md](../dev/writes.md)
   "Finalize → publisher residual" for details.
 - **D₂ parse-time rule**: a single mutation query is either
   insert/update-only or delete-only. Mixed → rejected with a clear
@@ -75,14 +75,14 @@ mutation proceeds normally.
 
 ## Tests added
 
-- `tests/runs.rs::partial_failure_leaves_target_queryable_and_unblocks_next_mutation`
+- `tests/writes.rs::partial_failure_leaves_target_queryable_and_unblocks_next_mutation`
   (replaces the old `partial_failure_observably_rolls_back_but_blocks_next_mutation_on_same_table`)
-- `tests/runs.rs::mutation_rejects_mixed_insert_and_delete_at_parse_time`
-- `tests/runs.rs::mixed_insert_and_update_on_same_person_coalesces_to_one_merge`
-- `tests/runs.rs::multiple_appends_to_same_edge_coalesce_to_one_append`
-- `tests/runs.rs::multi_statement_inserts_publish_exactly_once`
-- `tests/runs.rs::load_with_bad_edge_reference_unblocks_next_load`
-- `tests/runs.rs::load_with_cardinality_violation_unblocks_next_load`
+- `tests/writes.rs::mutation_rejects_mixed_insert_and_delete_at_parse_time`
+- `tests/writes.rs::mixed_insert_and_update_on_same_person_coalesces_to_one_merge`
+- `tests/writes.rs::multiple_appends_to_same_edge_coalesce_to_one_append`
+- `tests/writes.rs::multi_statement_inserts_publish_exactly_once`
+- `tests/writes.rs::load_with_bad_edge_reference_unblocks_next_load`
+- `tests/writes.rs::load_with_cardinality_violation_unblocks_next_load`
 
 ## Files changed
 
@@ -105,7 +105,7 @@ mutation proceeds normally.
 - `Cargo.toml` (workspace) + `crates/omnigraph/Cargo.toml` — added
   `datafusion = "52"` direct dep (transitively pulled by Lance
   already; required for `MemTable`).
-- `docs/dev/runs.md` — removed "Known limitation" section; documented
+- `docs/dev/writes.md` — removed "Known limitation" section; documented
   the new accumulator + D₂ + LoadMode::Overwrite residual.
 - `docs/dev/invariants.md` — mutation atomicity / read-your-writes status
   flipped to `upheld for inserts/updates`.
@@ -127,7 +127,7 @@ mutation proceeds normally.
   as legacy.
 - `docs/user/cli.md` — replaced the legacy `omnigraph run *` quickstart
   block with `omnigraph commit list/show`.
-- `docs/dev/testing.md` — extended the `runs.rs` row to cover the new
+- `docs/dev/testing.md` — extended the `writes.rs` row to cover the new
   staged-write contract tests; added the `staged_writes.rs` row.
 - `AGENTS.md` (CLAUDE.md symlink) — updated the atomic-per-query
   description and the L2 capability matrix row.