fix(sqli): HTML-escape description fields and harden qtLiteral

Fixes a SQL injection vulnerability where authenticated users could
break out of SQL string literals in COMMENT ON ... IS '<description>'
clauses by submitting an apostrophe-laden description through pgAdmin
dialogs. The original report covered domains; the patch expands the
fix to every site of the same pattern.

Three layers of defense:

1. Site fixes (16 places) — Replace '{{ x.description }}' with
   {{ x.description|qtLiteral(conn) }} across templates for domains,
   domain constraints, foreign tables, languages, event triggers,
   and the views OID-lookup query. Plumbs conn=self.conn through
   every render_template call that needed it. Also fixes a `{ % elif`
   Jinja typo in foreign-table schema diff that was preventing the
   elif branch from being reachable.

2. Driver hardening — qtLiteral (in utils/driver/psycopg3/__init__.py)
   used to silently return the raw unescaped value when conn was
   falsy. Now raises ValueError with a message pointing at the two
   fixes (render_template(..., conn=) or pass conn as the second
   argument). Surfaces this whole bug class loudly going forward,
   and immediately uncovered 8 latent plumbing bugs in
   schemas/__init__.py, schemas/functions/__init__.py,
   schemas/tables/utils.py, foreign_servers/__init__.py, and 7 sites
   in roles/__init__.py — all now fixed.

3. Regression tests (3 new files):
   - test_comment_description_sql_escaping.py — renders each
     previously-vulnerable template with an apostrophe-injection
     payload and asserts the escaped fragment is present (15
     scenarios).
   - test_sql_string_literal_lint.py — walks every *.sql template,
     flags every '{{ ... }}' single-quote-wrapped Jinja
     interpolation, and compares against a curated allowlist (75
     entries, each with a justification — OIDs, fixed enums,
     server-derived identifiers, SQL-comment headers, etc.). New
     occurrences fail the test until either qtLiteral is used or
     an allowlist entry is added.
   - test_qtliteral_requires_conn.py — unit test asserting the new
     fail-fast behavior.

Reported by Jasser Chebbi (j3seer).