feat(cli): modern Rich terminal styling across all modules

## Summary

Overhaul the CLI and all library modules to produce polished, modern
terminal output comparable to tools like uv, gh, and cargo. Rich was
already a declared dependency but barely used — this commit wires it
throughout every layer.

## Changes by layer

### semantica/cli.py — visual overhaul
- Add imports: `box`, `Panel`, `Rule`, `Syntax`, `Text` from Rich
- Add 7 style constants (`_BRAND`, `_KEY`, `_VAL`, `_DIM`, `_SUCCESS`,
  `_WARN_STY`, `_TABLE_BOX`) for a consistent colour palette
- `_ok()` now prefixes output with a green ✓ checkmark
- New `_info()` helper (neutral · bullet, respects --quiet)
- New `_warn()` helper (yellow ⚠ prefix, never suppressed)
- New `_pprint()` helper: renders dicts/lists as syntax-highlighted JSON
  (Rich Syntax, monokai theme) instead of raw Python repr; strings
  pass through unchanged; respects --quiet
- `info` command: banner replaced with a rounded Rich Panel showing
  version + tagline; component table uses SIMPLE_HEAD box
- All 7 table sites updated: `box=SIMPLE_HEAD`, `show_edge=False`,
  consistent `_KEY`/`_VAL` column styles (KG Stats, Reasoning Engines,
  Recent Decisions, Configured Backends, Backup Info, MCP Tools)
- `_run_build()`: `console.status(spinner="dots")` wraps the blocking
  build call; skipped under --quiet / --json
- `parse`, `extract`, `embed generate`, `reason run`, `reason explain`,
  `deduplicate`: each wraps its long-running operation in a status
  spinner, guarded by --quiet / --json
- All 30+ `console.print(result)` calls replaced with `_pprint()`
- All raw `[yellow]Warning:[/yellow]` and "not running" patterns
  replaced with the new `_warn()` / `_WARN_STY` style

### semantica/explorer/__init__.py
- Error messages use `Console(stderr=True)` with `[bold red]Error:[/bold red]`
- Graph loading wrapped in `console.status()` spinner
- Startup info replaced with a cyan-bordered Rich Panel showing URL,
  API docs, and health endpoint

### Library internals — replace print() with structured logger calls
All modules below had active `print()` calls that bypassed the logging
framework, corrupted spinners, and polluted stdout in piped/programmatic
use. All replaced with appropriate `self.logger.*` calls:

- `semantica/kg/graph_builder.py` — 23 calls: entity resolution
  progress, graph structure steps, GraphStore persistence timing, and
  the two `='*60` completion banners → `self.logger.info/debug()`
- `semantica/semantic_extract/methods.py` — 4 verbose-mode debug
  prints → `logger.debug()`
- `semantica/semantic_extract/relation_extractor.py` — progress +
  error prints → `self.logger.debug/warning()` with `exc_info`
- `semantica/semantic_extract/triplet_extractor.py` — same pattern
- `semantica/semantic_extract/semantic_network_extractor.py` — batch
  error prints → `self.logger.warning/error()`
- `semantica/semantic_extract/coreference_resolver.py` — error print
  → `self.logger.error()`
- `semantica/semantic_extract/providers.py` — debug print →
  `self.logger.debug()`

### Tooling
- `benchmarks/benchmarks_runner.py`: Rule banner, ✓/✗/⚠ status lines,
  Rule separators around regression alert
- `benchmarks/infrastructure/compare.py`: removed manual ANSI escape
  codes; comparison output is now a Rich Table with SIMPLE_HEAD;
  summary uses coloured Rule + styled SUCCESS/FAILURE messages
- `cookbook/advanced/snowflake_ingestion_examples.py`: `_section()`
  helper using Rule; tabular data rendered as Rich Table; result lines
  use ✓/✗/⚠ prefixes; logger.error already present, retained
- `docs_check.py`: `pass`/`FAIL` lines use `[bold green]` /
  `[bold red]`; summary uses styled output

## Tests
- `tests/test_cli_commands.py`: fix 3 pre-existing mock mismatches
  - `test_kg_stats_json_with_mock`: mock now uses `compute_metrics()`
    (the method the code actually calls) instead of `get_statistics()`
  - `test_dry_run_not_needed_extract_is_read_only` and
    `test_stdin_input`: mock now provides `NERExtractor`,
    `RelationExtractor`, `TripletExtractor`, `EventDetector`
    (the classes the code imports) instead of `SemanticAnalyzer`
  Result: 230/230 tests pass (was 227/230)
- `tests/verify_rich_cli.py`: new verification script; exercises all
  14 command groups (92 --help checks, table rendering, dry-run
  formatting, --json mode, _pprint helper); 111 pass, 0 fail

docs_check.py

@@ -8,10 +8,13 @@ import re
 import sys
 from typing import Any, Callable, cast
 
+from rich.console import Console
+
 DOCS = "docs"
 ALL_MD: list[str] = glob.glob(f"{DOCS}/**/*.md", recursive=True)
 
 failures: list[str] = []
+console = Console()
 
 
 def check(label: str) -> Callable[[Callable[[], list[str]]], None]:
@@ -19,12 +22,12 @@ def check(label: str) -> Callable[[Callable[[], list[str]]], None]:
     def decorator(fn: Callable[[], list[str]]) -> None:
         issues = fn()
         if issues:
-            print(f"FAIL  {label}")
+            console.print(f"[bold red]FAIL[/bold red]  {label}")
             for msg in issues:
-                print(f"      - {msg}")
+                console.print(f"[dim]      - {msg}[/dim]")
             failures.extend(issues)
         else:
-            print(f"pass  {label}")
+            console.print(f"[bold green]pass[/bold green]  {label}")
     return decorator
 
 
@@ -162,9 +165,9 @@ def _() -> list[str]:
 
 
 # ── Summary ───────────────────────────────────────────────────────────────────
-print()
+console.print()
 if failures:
-    print(f"FAILED  {len(failures)} issue(s) found")
+    console.print(f"[bold red]FAILED[/bold red]  {len(failures)} issue(s) found")
     sys.exit(1)
 else:
-    print("All checks passed")
+    console.print("[bold green]All checks passed[/bold green]")