metis: file DST gaps as follow-up bugs (T-0342/0343/0344)

[dylanbstorey]

Docs-only. Files the 12 remaining Temporal DST scenarios (out of scope for the +30 non-DST close in #88) as three triageable backlog bugs sharing one root cause (no embedded IANA tzdata):

• GQLITE-T-0342 — duration across a DST transition ignores the gained/lost hour (Temporal10 [8], 8 examples)
• GQLITE-T-0343 — named-zone offset uses a coarse month approximation, not historical rules (Temporal3 [10], 2); documents the −52-regression trap so the next attempt avoids it
• GQLITE-T-0344 — datetime string parse doesn't resolve named-zone historical/LMT offset, e.g. 1818 Stockholm = +00:53:28 (Temporal2 [6], 2); the foundational embed IANA tzdata item the other two depend on

Each carries repro, expected vs actual, root cause, and acceptance criteria. Cross-linked from GQLITE-T-0341 / GQLITE-I-0049.