[NF-46] [FRONTEND] Governance Proposal Deep-Dive/History Archive

[wumibals]

Overview

The existing (once GF-16 merges) /governance page shows a basic proposal history list. This issue adds a richer, dedicated archive page with per-proposal analytics for anyone wanting to audit the Strategist/Guardian's track record in depth.

Problem

A basic list of past proposals with status doesn't let anyone easily answer questions like: how often are proposals vetoed, what's the average time-to-execution, which pools has the Strategist favored over time, or how has any single pool's allocation percentage changed across multiple proposals. That requires cross-referencing many individual proposals, which the basic list doesn't support.

Proposed Solution

• New page app/src/app/governance/history/page.tsx, linked from the main /governance page.
• Aggregate stats: veto rate, average time-to-execution, proposal count over time (chart).
• Per-pool allocation history chart: how a specific pool's target percentage has changed across every proposal that touched it, over time.
• Full-text/filterable proposal table (by pool, by status, by date range), each row linking to the transaction on Stellar Expert.

Acceptance Criteria

• Aggregate stats (veto rate, average execution time) are computed correctly from real proposal history
• Per-pool allocation history chart accurately reflects the sequence of allocation changes for a selected pool
• Table filtering by pool/status/date range works correctly and combinably
• Every proposal row links to a working Stellar Expert transaction URL
• Page handles the zero-history case (new/low-activity protocol) without a broken empty chart