feat!: remove has_ai_task and the task build reasons - #29085

Removes every in-repo Tasks client: the `coder exp tasks` CLI command
family, the tasks scaletest runner, and the task-driven triage
automation (`traiage.yaml`, `code-review.yaml`,
`classify-issue-severity.yml`, `scripts/traiage.sh`). Triage runs
through `triage-via-chat-api.yaml` and coder/create-agent-chat-action
instead.

**Stack context:** Coder Tasks removal stack (CODAGT-642): #28743
frontend → #28788 CLI → #28789 API → #28790 provisioner → #29084
notifications and usage → #29085 build reasons → #29086 tables → #28750
permissions. The last four PRs replace the single data-drop migration
that used to live in #28750; each carries one concern and a focused
migration test.

**Why:** clients come off before the API they call. After this layer
nothing in the repo invokes the Tasks API outside coderd itself.

**What to scrutinize:** all but three files are whole-file deletions.
`triage-via-chat-api.yaml` gets a comment fix. `NavbarView.tsx` and its
stories carry two small repairs to the frontend layer below (unused
`user` prop, stale `TasksFilter` story wiring) so the stack lints clean
from this layer up; they rebase away if folded into #28743.

**Validation:** `go build ./...`, `go test ./cli -run TestCommandHelp`,
site tsc, pre-commit hooks (gen, fmt, lint).

**Size:** +4/-6,938 over 42 files; effectively pure deletion, so it
reads much faster than the line count suggests.

> Created by Xum (AI agent) on behalf of @ibetitsmike.

Removes the Tasks API and task orchestration from coderd and codersdk:
the `/api/v2/tasks` handlers, task middleware and search filters, task
name generation, autobuild pause/resume logic, task notification
enqueues, telemetry, and the codersdk task types. Regenerates apidoc,
the API reference docs, and `typesGenerated.ts`.

**Breaking change:** the Tasks API is removed; requests to
`/api/v2/tasks` fail. Tasks was deprecated in v2.34.

**Stack context:** Coder Tasks removal stack (CODAGT-642): coder#28743
frontend → coder#28788 CLI → coder#28789 API → coder#28790 provisioner → coder#29084
notifications → coder#29085 build reasons → coder#29086 tables → coder#28750
permissions. The last four PRs replace the single data-drop migration
that used to live in coder#28750; each carries one concern and its own
migration number.

**Why:** with the UI (coder#28743) and CLI (coder#28788) gone, this deletes the
server surface. Database tables, RBAC, and notification templates stay
until the top of the stack so every layer builds and migrates
independently.

**What to scrutinize:**
- The `enable-ai-tasks` option is removed outright (review feedback):
configs still carrying `enableAITasks` fail to parse until the key is
deleted.
- provisionerdserver now writes `HasAITask: false` on template/build
flags; the column and these lines are dropped in coder#29085.
- `codersdk.ResourceTypeTask` stays so audit logs recorded before the
removal keep rendering.

**Validation:** `go build ./...`, `go vet ./...`, `go test
./codersdk/...`, site biome and tsc, CLI goldens regenerated, pre-commit
hooks.

**Size:** +242/-10,792 over 76 files; additions are regenerated
docs/goldens and test fixture updates.

> Created by Xum (AI agent) on behalf of @ibetitsmike.

Removes AI task support from the provisioner protocol: the task-related
proto fields, terraform scanning for `coder_ai_task` resources, echo
provisioner support, the regenerated `.pb.go` and
`provisionerGenerated.ts`, and the terraform testdata that exercised
them. The provisioner API version change lives in
`provisionerd/proto/version.go`.

**Stack context:** Coder Tasks removal stack (CODAGT-642): #28743
frontend → #28788 CLI → #28789 API → #28790 provisioner → #29084
notifications and usage → #29085 build reasons → #29086 tables → #28750
permissions. The last four PRs replace the single data-drop migration
that used to live in #28750; each carries one concern and a focused
migration test.

**Why:** the proto fields lost their last consumer in #28789; this
deletes the producer side and the wire format.

**What to scrutinize:** the proto/version handling, and that
`coder_ai_task` resources in existing templates are now ignored rather
than errors (template imports simply no longer scan for them).

**Validation:** `go build ./...`, `go test ./provisionersdk/...
./provisionerd/...`, `go test ./provisioner/terraform -run
TestConvertResources`, provisioner list golden regenerated, site tsc,
pre-commit hooks.

**Size:** +580/-1,286 over 76 files; most files are mechanical testdata
and generated-code updates.

> Created by Xum (AI agent) on behalf of @ibetitsmike.

Removes the six Coder Tasks notification templates (their preferences
and inbox history go with them via cascade) and the
`preference_task_notification_alert_dismissed` user setting with its two
queries. The `task` value of `ai_seat_usage_reason` stays: seats
consumed through tasks remain consumed, and remapping their reason would
misstate billing history.

**Breaking change:** migration 000592 deletes data. The down migration
restores the template definitions, not the deleted preferences or
notification history.

**Review changes:** dropped the `ai_seat_state` remap and enum swap and
the migration unit test (both per review); moved the migration from
000591 to 000592 because main took 000591.

**Stack context:** Coder Tasks removal stack (CODAGT-642): #28743
frontend → #28788 CLI → #28789 API → #28790 provisioner → **#29084
notifications** → #29085 build reasons → #29086 tables → #28750
permissions. The last four PRs replace the single data-drop migration
that used to live in #28750; each carries one concern and its own
migration number.

> Created by Xum (AI agent) on behalf of @ibetitsmike.