Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Running opencode on airgapped/offline machines currently requires a pile of separate knobs — OPENCODE_DISABLE_AUTOUPDATE, OPENCODE_DISABLE_MODELS_FETCH + OPENCODE_MODELS_PATH, .npmrc offline=true, a pre-seeded ripgrep — and still trips over paths those don't cover. Two flags the docs mention (OPENCODE_DISABLE_LSP_DOWNLOAD, OPENCODE_DISABLE_DEFAULT_PLUGINS) are no-ops in v2: they only exist in the docs.

Proposal: one explicit env switch, OPENCODE_OFFLINE=1, that makes every runtime-network feature behave as if offline:

• skip the update check (same as OPENCODE_DISABLE_AUTOUPDATE)
• disable the models.dev fetch (bundled snapshot / OPENCODE_MODELS_PATH still serve the catalog)
• force the npm/Arborist stack to offline mode (cache-only, instant failure; explicit user npm config still wins)
• skip the ripgrep download (PATH lookup only, clear error otherwise)

Explicit flag only, no auto-detection. I have a working implementation with tests ready to open as a PR if the design is acceptable (fork branch PJ-Zetier/opencode@offline-startup-bounds, commit b5bbf75) — happy to adjust naming and scope.