feat(daemon): add remote messaging control

[rmacomber]

Summary

• add opt-in Telegram and WhatsApp remote control for vixd
• require explicit feature/config enablement plus sender allowlists before accepting remote prompts
• run remote prompts in isolated headless sessions and deny unattended permission/plan interactions
• document remote-control configuration in the README

PR cleanliness

• Based on upstream/main at c25f0d73ecc7ab55a540892c8c061ea8b725fc15
• Contains one feature commit: b730897 feat(daemon): add remote messaging control
• Does not include PR feat(config): add code-explorer default agent #38 (21afebd73e86a4bc157796e39076ae0cf456a09e is not an ancestor)
• Does not include PR feat(config): add code-explorer default agent #38's file: internal/config/defaults/agents/code-explorer.md

Verification

• gofmt check passed for changed Go files
• go build ./cmd/vix ./cmd/vixd
• go test ./cmd/vixd ./internal/config
• go test ./internal/daemon -run 'Test(AuthorizedRemoteIDRequiresAllowlist|RemoteSessionOptionsDisableAutomaticPermissions|RemoteUnattendedEventsDoNotAutoApprove|TelegramSendMessageRedactsBotTokenFromErrors|WhatsAppStartFailsWhenWebhookAddrAlreadyBound|TelegramSendMessagePostsChatIDAndText|TelegramGetUpdatesRedactsBotTokenFromErrors|WhatsAppWebhookVerificationAndAllowlist)'
• go test ./cmd/vix ./cmd/vixd ./internal/agent ./internal/auth ./internal/config

Note: full go test ./... currently fails in pre-existing internal/daemon tests unrelated to this branch: missing testdata/tmp.go fixture expectations in VFS/minify tests and Landlock sandbox environment assumptions. The changed remote-control tests pass.