feat(ui): dedicated space-less org proposals route

[wa0x6e]

Follow-up to #2103 / #2217.

Org proposals currently render under per-governor routes (/org/arbitrum/<space>/proposals, whitelabel /core-gov), with the Spaces filter persisted as ?space=<address>. Route path and query param encode the same axis and can contradict (e.g. /treasury-gov?space=0xCore... shows Core proposals on the Treasury URL), and the URL duplicates the space address.

Proposal:

• Add a space-less route (e.g. /org/:org/proposals, whitelabel equivalent) rendering Organization/Proposals.vue directly.
• Per-governor proposals routes redirect or link into it.
• The Spaces filter query param becomes the only space axis.

Depends on #2217 (org view must exist standalone).