docs: rewrite Semantic Querying concept with imperative-vs-declarative diagram (#156)

* docs: rewrite Semantic Querying concept with imperative-vs-declarative diagram

Reframe semantic-layer-internals.mdx around the contract the semantic
layer offers an agent: declare what you want (a Semantic Query), KTX
figures out how to compute it. Replaces the old "Context-Aware SQL"
framing with a clear imperative-vs-declarative narrative.

Adds a React Flow component (semantic-layer-flow.tsx) that contrasts a
buggy 4-table agent-authored SQL (chasm trap, LEFT-JOIN-in-WHERE,
hardcoded DATE_TRUNC) against the chasm-safe per-fact CTE SQL the
planner actually emits, including the outer GROUP BY over the requested
dimensions. Both lanes converge into a shared warehouse node and each
SQL card now has parallel bullet notes (failures on the left, KTX
behavior on the right).

Side fixes bundled in:
- include the /ktx basePath in the favicon metadata so the icon resolves
  under the production prefix
- migrate docs-site/middleware.ts to docs-site/proxy.ts (Next 16 rename)
- redirect / to /ktx/docs/getting-started/introduction so the apex docs
  URL works
- add tests covering the apex redirect, the favicon basePath, and the
  middleware-to-proxy rename
- propagate the Semantic Query terminology across the ktx-sl CLI
  reference, the context-layer concept page, and the agent-clients /
  primary-sources integration pages

* Fix CI dead-code failures

* docs-site: polish semantic-layer-internals code blocks and flow diagram

- Make CodeBlock a server component so children traverse synchronously
  under React 19 RSC streaming; previously extractText returned "" in
  dev SSR, leaving code blocks empty.
- Add custom JSON/YAML/SQL/code-like tokenizers with theme-aware token
  classes; drop the colored file-glyph dot and gradient tab-head.
- Tighten tab-head: subtle grey background, smaller monospace filename
  in muted grey, smaller rectangular language pill placed to the left
  of the filename.
- Polish the React Flow semantic-layer diagram (controls, fit-view
  padding, edge types).

* docs-site: annotate imperative SQL, add section anchor, drop ClickHouse

- Wire numbered red badges to each problematic span in the "Without KTX"
  SQL with hover sync between SQL gutter, lines, and the notes list.
- Add #imperative-vs-declarative anchor on the flow section header so
  the eyebrow link is shareable; reveals a # glyph on hover/focus.
- Align the compiled-SQL note dots to the first-line midpoint
  (mt-[6px] instead of mt-1) so 4px dots sit at y=8 in a 16px line.
- Remove all ClickHouse references from docs-site (primary-sources,
  quickstart, ktx-setup, contributing, agents-setup, mechanics test,
  warehouse drivers in the flow diagram).

* test: drop ClickHouse contributing-docs assertion

Align the workspace-package mirror test with the ClickHouse removal
from docs-site (75907eb). The connector-clickhouse package still
exists in packages/, but contributing.mdx no longer lists it, so the
test that mirrored docs against the workspace was failing.

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

@@ -103,7 +103,7 @@ runtime features are missing.
 
 | Flag | Description |
 |------|-------------|
-| `--database <driver>` | Database driver to configure; repeatable. Choices: `sqlite`, `postgres`, `mysql`, `clickhouse`, `sqlserver`, `bigquery`, `snowflake` |
+| `--database <driver>` | Database driver to configure; repeatable. Choices: `sqlite`, `postgres`, `mysql`, `sqlserver`, `bigquery`, `snowflake` |
 | `--database-connection-id <id>` | Existing selected connection id; repeatable. With `--database` or `--database-url`, connection id for the new connection. |
 | `--database-url <url>` | URL, `env:NAME`, or `file:/path` for one new URL-style database connection; also used as the SQLite path |
 | `--database-schema <schema>` | Database schema or dataset to include; repeatable |

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

@@ -20,7 +20,7 @@ ktx sl <subcommand> [options]
 | `list` | List semantic-layer sources |
 | `search <query>` | Search semantic-layer sources |
 | `validate <sourceName>` | Validate a semantic-layer source against the database schema |
-| `query` | Compile or execute a semantic-layer query |
+| `query` | Compile or execute a Semantic Query |
 
 ## Options
 
@@ -52,7 +52,7 @@ ktx sl <subcommand> [options]
 | Flag | Description | Default |
 |------|-------------|---------|
 | `--connection-id <id>` | KTX connection id | - |
-| `--query-file <path>` | JSON semantic-layer query file | - |
+| `--query-file <path>` | JSON Semantic Query file | - |
 | `--measure <measure>` | Measure to query; repeatable (at least one required) | - |
 | `--dimension <dimension>` | Dimension to include; repeatable | - |
 | `--filter <filter>` | Filter expression; repeatable | - |
@@ -67,7 +67,7 @@ ktx sl <subcommand> [options]
 | `--max-rows <n>` | Maximum rows to return when executing | - |
 
 `sl query` requires at least one `--measure` unless `--query-file` is set.
-`--query-file` should point to a JSON semantic-layer query object.
+`--query-file` should point to a JSON Semantic Query object.
 
 ## Examples