fix(activation): always INSTALL iceberg even when bundled

[benben]

Problem

After #645 bundled the iceberg extension into the worker image, iceberg-only tenant activation still hangs past the activate-tenant deadline. The bundle is correct — /data/extensions/v1.5.3/linux_arm64/iceberg.duckdb_extension is in place (the bootstrap seeded it from /app/extensions/...) — but db.Exec("LOAD iceberg") blocks for the full ~60s with no progress and no DuckDB-level log, until the CP cancels and the worker is retired.

Why: LoadExtensions skips INSTALL whenever hasBundledExtensionBinary returns true:

if shouldInstallExtension(name) { db.Exec("INSTALL " + installCmd) }
db.Exec("LOAD " + name)

That works for httpfs, ducklake, json, postgres_scanner — LOAD against the seeded extension_directory file just works. It does not work for iceberg: without a prior INSTALL, DuckDB's internal extension metadata leaves LOAD iceberg blocked indefinitely, even with the binary already in the cache. So the very INSTALL the bundle was meant to spare us turns into the same silent stall when the bundle deletes the call.

Live evidence on mw-dev (ben-ext-ice, build 2f2f38d = #645):

step=count-catalogs       elapsed=172ns
step=load-iceberg-extension elapsed=1.5ms
… (no further activity for ~60s) …
worker shutting down

Fix

Special-case iceberg in shouldInstallExtension so INSTALL runs even when the binary is bundled. With the file already in extension_directory, INSTALL is a cheap no-op — DuckDB sees the cached file and skips the CDN download — so the bundle benefit is preserved (no first-load fetch from the CDN) while LOAD now finds the extension already installed.

The upstream-overwrite risk that motivates skipping INSTALL for the PostHog forks (httpfs, ducklake) doesn't apply: we bundle the same stock iceberg build the DuckDB repository would serve.

Test plan (mw-dev after deploy)

• ben-ext-ice activates within the deadline.
• Iceberg-only SELECT 1 succeeds; CREATE TABLE iceberg.public.<t> / INSERT / SELECT round-trips.
• The "both" combos (already passing for iceberg + DuckLake) remain green.

🤖 Generated with Claude Code