Route Parsar Agent execution through Core

[SaladDay]

Parsar's product now executes Agents exclusively through the public Core Agents API, replacing direct daemon, HTTP-agent and sandbox execution paths. Business members, Skills/MCP asset management, permissions, conversations, scheduling and the product database remain in Parsar.

• Use workspace-scoped Core credentials, frozen Session/input bindings, durable Turn/Items observation, cancellation, recovery and idempotent usage accounting.
• Keep Parsar's sidebar and member/conversation flows. Environment templates follow the official contract; unsupported runtime activation is explicit. Asset import or OAuth does not imply runtime availability.
• Remove replaced execution routes and reject obsolete connectors without compatibility fallbacks. Include product migration, regenerated contracts, architecture documentation and the product image's Core client build dependency.

Validation: full make check passed on Linux zju_a100_2 against code commit 3007d02e (exit 0). Product Store/dev database suites and independent connector/isolation/recovery tests passed. Live MiniMax-M3 via Core verified conversation creation, consecutive input, cancellation, restart recovery, deletion cleanup and explicit unsupported-model failure. Browser inspection confirmed Parsar's existing UI structure and capability availability labels. Product image, Go/Store/Web/CLI, generated contracts and Core official-client/container CI passed on that code commit.

After the fresh-subagent capacity limit was reached, the user explicitly authorized reusing an existing reviewer. Independent re-review of the complete diff found no blocking code issue and reran focused database/recovery/isolation tests. This is recorded as a re-review, not a fresh-context review.

Limitations: the baseline public Core API cannot immediately cancel pending environment preparation; product cancellation intent remains durable until Core admits cancellation. One MiniMax packaged-native-tools test is prerequisite-skipped and is not counted as passed. Existing macOS native-runtime and Linux-specific Rust failures are documented; no unrelated platform fixes were added. No Core feature expansion or mx redeployment is included.

See object/protocol mapping and acceptance evidence, environment and reproductions.

Validation baseline is d8ed9d42; the later Core initialization change #709 is not included in this branch's acceptance evidence. This PR is submitted for review, not automatic merge or deployment.