feat(cli): shell completion for commands, flags, and entity names (#244)

* feat(completion): complete known argument values

* fix(completion): hide Commander-hidden subcommands from completions

Replace the `__`-prefix name heuristic with Commander's `_hidden` flag so
internal subcommands registered with { hidden: true } (e.g. `mcp serve-internal`)
are excluded from completions, mirroring `ktx --help`.

* test: cover wiki and sl read command routing

* test: cover raw wiki and sl reads

* feat: add wiki read command

* feat: add sl read command

* feat: complete read command entity names

* docs: document wiki and sl read commands

* test: include read commands in command tree

* feat(sl): read and validate unique sources by name

* feat(sl): make read and validate connection id optional

* fix(completion): dedupe semantic source names

* docs(sl): document connection-optional read and validate

* fix(sl): require connection id for query command

* docs(sl): clarify query connection requirement

* fix(completion): don't resolve option values as subcommands

resolveCommand skipped flag tokens but not the value consumed by a
value-taking option in the `--flag value` form, so a connection id like
`query` was matched as the `sl query` subcommand and yielded no `sl`
completions. Track value-taking options and skip their consumed value
before matching subcommands.

* test(telemetry): assert first-run notice via TELEMETRY_NOTICE constant

CI (which tests this branch merged with main) failed because #243 changed
the first-run notice wording in identity.ts (dropped "anonymous") but left
this test grepping for the old literal 'ktx collects anonymous usage data',
so indexOf returned -1. Assert against the exported TELEMETRY_NOTICE
constant instead so the test tracks the source of truth and cannot drift
when the notice text changes again.

docs-site/content/docs/cli-reference/ktx.mdx

@@ -36,9 +36,11 @@ ktx
   wiki
     list
     search <query>
+    read <key>
   sl
     list
     search <query>
+    read <sourceName>
     validate <sourceName>
     query
   sql
@@ -57,6 +59,7 @@ ktx
       stop
       status
     reindex
+  completion <shell>
 ```
 
 The public context-build entrypoint is `ktx ingest [connectionId]` or
@@ -97,6 +100,10 @@ ktx ingest
 ktx sl "revenue"
 ktx wiki "revenue recognition"
 
+# Print a known wiki page or semantic source
+ktx wiki read revenue-definitions
+ktx sl --connection-id warehouse read orders
+
 # Execute read-only SQL
 ktx sql --connection warehouse "select count(*) from public.orders"