ADR-0024 Phase F (full) step 2: usage via CommandNode.usage_ids

Migrates parse-error usage-block rendering from the legacy
`dsl::usage::matched_entry` (which scanned a `Vec<Token>` for the
first matched Keyword) to walker-side lookup driven by each
`CommandNode`'s `usage_ids` slice.

`CommandNode.usage_id: Option<&'static str>` becomes
`usage_ids: &'static [&'static str]`. Multi-form families
(`drop`, `add`, `show`) carry every variant — `drop` lists
table/column/relationship templates; `add` lists column /
relationship; `show` lists data / table. The single-shape
commands carry their single catalog key.

App-lifecycle CommandNodes had pointed at non-existent
`parse.usage.app.*` keys (never noticed because the field was
unused); they now point at the real catalog entries
(`parse.usage.quit`, `parse.usage.help`, …).

New helpers in `dsl::grammar`:
- `usage_keys_for_input(source) -> Option<(entry_word, usage_ids)>`
  resolves the first identifier-shape token to a CommandNode and
  returns its usage_ids list. Used by `app::render_usage_block`
  and `input_render::ambient_hint`.
- `entry_words_alphabetised() -> Vec<&'static str>` replaces
  `dsl::usage::entry_keywords_alphabetised`.

`dsl::usage` is deleted. The "available commands:" fallback in
`render_usage_block` now formats entry words as `` `<word>` ``
directly (matching the `parse.token.keyword.*` catalog renders);
the per-keyword catalog wrappers will collapse in the next step
(ADR-0024 §cleanup-pass §F).

`parse_command` and `parse_tokens` slim down:
- `parse_command(input)` no longer pre-lexes — the walker scans
  source bytes directly.
- `parse_tokens` (internal-only `pub` for "future I3/I4 work")
  is removed; its body folded into `parse_command`.
- `unknown_command_error` reads the walker registry directly.

Touched modules also drop their `crate::dsl::lexer::lex` and
`crate::dsl::usage` imports: `app.rs`, `input_render.rs`,
`completion.rs`.

Tests: 852 passing, 0 failing, 1 ignored (down from 860 because
the 8 `dsl::usage::tests::*` tests are gone with the module).

src/dsl/grammar/data.rs

@@ -529,7 +529,7 @@ pub static SHOW: CommandNode = CommandNode {
     shape: SHOW_SHAPE,
     ast_builder: build_show,
     help_id: Some("data.show"),
-    usage_id: Some("parse.usage.show"),
+    usage_ids: &["parse.usage.show_data", "parse.usage.show_table"],
     hint_mode: None,
 };
 
@@ -538,7 +538,7 @@ pub static INSERT: CommandNode = CommandNode {
     shape: INSERT_SHAPE,
     ast_builder: build_insert,
     help_id: Some("data.insert"),
-    usage_id: Some("parse.usage.insert"),
+    usage_ids: &["parse.usage.insert"],
     hint_mode: None,
 };
 
@@ -547,7 +547,7 @@ pub static UPDATE: CommandNode = CommandNode {
     shape: UPDATE_SHAPE,
     ast_builder: build_update,
     help_id: Some("data.update"),
-    usage_id: Some("parse.usage.update"),
+    usage_ids: &["parse.usage.update"],
     hint_mode: None,
 };
 
@@ -556,7 +556,7 @@ pub static DELETE: CommandNode = CommandNode {
     shape: DELETE_SHAPE,
     ast_builder: build_delete,
     help_id: Some("data.delete"),
-    usage_id: Some("parse.usage.delete"),
+    usage_ids: &["parse.usage.delete"],
     hint_mode: None,
 };
 
@@ -565,6 +565,6 @@ pub static REPLAY: CommandNode = CommandNode {
     shape: REPLAY_PATH,
     ast_builder: build_replay,
     help_id: Some("data.replay"),
-    usage_id: Some("parse.usage.replay"),
+    usage_ids: &["parse.usage.replay"],
     hint_mode: None,
 };