feat: add Linear integration (#736)

* feat: add Linear integration

Mirrors the existing Jira integration so a workspace can connect to Linear
with a personal API key, browse and search issues, and start a Kandev task
from any issue. Backend uses Linear's GraphQL API with a workspace-scoped
config + secret store and a 90s auth-health poller; the frontend adds a
settings page, an issue dialog with state transitions, link/import buttons
in the task UI, and a paginated /linear browse page with a Start task flow.

* fix(linear): address PR review feedback

- Route httpListStates through Service.ListStates instead of clientFor
- Extract repeated workspace_id required string into a constant
- Log GetConfig errors during credential resolution instead of dropping them
- Clear popover error state on close in import + link buttons
- Pick the first workflow with steps in the quick task launcher (don't hard-pin to workflows[0])
- Reset useLinearEnabled state on workspace change via tag-based pattern
- Add cursor-pointer to anchor + Link elements per project convention
- Add tests: handlers_test.go, linear-api.test.ts, use-linear-enabled.test.ts, linear-issue-common.test.tsx
- Document internal/jira and internal/linear in CLAUDE.md/AGENTS.md

* fix(linear): address second-round PR review feedback

- Round Linear's fractional state position instead of truncating it via
  int(math.Round(s.Position)) so adjacent fractional positions don't collapse
- Force LinearSettings to remount on workspace change with key={id} so the
  previous workspace's config / form / testResult / teams cannot bleed into
  the next workspace before the new fetches settle
- Broaden the legacy-value useLinearEnabled test to cover "true", "1", "yes",
  and "legacy" so a regression to strict value === "true" would fail

* fix(linear): address third-round PR review feedback

- Propagate context.Canceled / context.DeadlineExceeded from ListStates in
  GetIssue instead of swallowing them — a caller cancellation must not return
  a partial-success response
- Drop the one-off contains() test helper in handlers_test.go and use
  strings.Contains directly so the assertion is self-documenting
- Add getLinearIssue URL-shape test that locks identifier-as-path-segment
  vs workspaceId-as-query-param so accidentally swapping them would fail

* test(linear): extract repeated literals in linear-api.test.ts

Pulls "ws-1", the API base URL, and the auth-method literal into module-
level constants so the assertions read as the route shape they care about
and the duplicate-strings ESLint rule (currently warn, threshold 4)
stays quiet as the file grows.

---------

Co-authored-by: Kandev Agent <agent@kandev.dev>

apps/web/components/task-create-dialog-form-body.tsx

@@ -14,6 +14,7 @@ import {
   computeBranchPlaceholder,
 } from "@/components/task-create-dialog-fresh-branch";
 import type { JiraTicket } from "@/lib/types/jira";
+import type { LinearIssue } from "@/lib/types/linear";
 
 type SelectorOption = {
   value: string;
@@ -360,8 +361,23 @@ export type DialogPromptSectionProps = {
   enhance?: { onEnhance: () => void; isLoading: boolean; isConfigured: boolean };
   workspaceId?: string | null;
   onJiraImport?: (ticket: JiraTicket) => void;
+  onLinearImport?: (issue: LinearIssue) => void;
 };
 
+// importBindings collapses the optional Jira/Linear import callbacks into the
+// shape TaskFormInputs expects, dropping integrations that aren't applicable
+// (session mode, started tasks, or no callback wired). Keeps DialogPromptSection
+// below the cyclomatic-complexity bar.
+function importBindings<T>(
+  enabled: boolean,
+  workspaceId: string | null,
+  isPassthroughProfile: boolean,
+  onImport: ((value: T) => void) | undefined,
+) {
+  if (!enabled || !onImport) return undefined;
+  return { workspaceId, disabled: isPassthroughProfile, onImport };
+}
+
 export function DialogPromptSection({
   isSessionMode,
   isTaskStarted,
@@ -373,8 +389,10 @@ export function DialogPromptSection({
   enhance,
   workspaceId,
   onJiraImport,
+  onLinearImport,
 }: DialogPromptSectionProps) {
-  const showJiraImport = !isSessionMode && !isTaskStarted && !!onJiraImport;
+  const importsEnabled = !isSessionMode && !isTaskStarted;
+  const ws = workspaceId ?? null;
   return (
     <>
       <TaskFormInputs
@@ -390,15 +408,8 @@ export function DialogPromptSection({
         onEnhancePrompt={enhance?.onEnhance}
         isEnhancingPrompt={enhance?.isLoading}
         isUtilityConfigured={enhance?.isConfigured}
-        jiraImport={
-          showJiraImport && onJiraImport
-            ? {
-                workspaceId: workspaceId ?? null,
-                disabled: isPassthroughProfile,
-                onImport: onJiraImport,
-              }
-            : undefined
-        }
+        jiraImport={importBindings(importsEnabled, ws, isPassthroughProfile, onJiraImport)}
+        linearImport={importBindings(importsEnabled, ws, isPassthroughProfile, onLinearImport)}
       />
       {isPassthroughProfile && hasDescription && (
         <p className="text-xs text-amber-500">Prompt ignored — passthrough mode active</p>