build: update DuckLake to v1.0-posthog.6

[bill-ph]

Summary

• update current Duckgres image, worker image, scenario, and e2e pins to DuckLake v1.0-posthog.6
• update the e2e extension-version assertion to 49ec0dc8

The release is built from DuckLake commit 49ec0dc880a749e059594ee699c87ba3a9f88524.

Verification

• just test-unit
• just lint
• verified both Linux release binaries against the published SHA256SUMS
• loaded the released Linux arm64 binary in Duckgres and confirmed duckdb_extensions() reports 49ec0dc8
• ran a PostgreSQL-backed DuckLake reproduction with three separate TIMESTAMPTZ data files; the narrow day-range query returned one row and EXPLAIN ANALYZE reported Total Files Read: 1

[github-actions]

Test Impact Plan

Deterministic summary of how this PR changes tests, CI runners, and coverage-risk signals.

Summary

Area	Added	Changed	Deleted
Test files	0	1	0
E2E/journey files	0	0	0
Workflow files	0	3	0

Signals

• Test cases: +0 / -0
• Assertions: +0 / -0
• Skips or known failures added: 0
• Workflow continue-on-error added: 0
• Workflow path filters added: 0
• Test commands removed from justfile: 0
• E2E/journey retry lines added: 0

Coverage risk: neutral or increased

No coverage-reduction warnings detected.