feat(auth): Microsoft OAuth sign-in/link + self-serve signup via Google/Microsoft

Wave 7. Mirrors the existing Google ID-token-exchange pattern (Program.cs
smart-scheme dispatch, JWT bearer scheme, AuthController exchange/link/
unlink endpoints, ApplicationUser fields, reconciler columns) for
Microsoft Entra ID + personal accounts via the multi-tenant "common"
endpoint.

Google/Microsoft sign-in previously only worked for accounts already
linked to an existing local user -- there was no way to actually sign
up via OAuth. Both exchange endpoints now create a new user when no
match is found and Auth:AllowRegistration is true, same gate as
email/password registration.

Frontend: new MicrosoftAuthCard (MSAL popup flow -- Microsoft has no
vanilla-JS equivalent to Google's Identity Services script) wired into
the login page's provider tabs and the profile page's account-linking
section. REACT_APP_MICROSOFT_CLIENT_ID env var, Auth:MicrosoftClientId
config gate on the backend.

job-tracker-ui/src/i18n/translations.ts

@@ -628,6 +628,26 @@ export const translations = {
     googleScriptLoadFailed: "Google auth script failed to load.",
     googleUnlinked: "Google account unlinked.",
     googleUnlinkFailed: "Failed to unlink Google account.",
+    microsoftAccountTitle: "Microsoft account",
+    microsoftSetupHint: "Set `REACT_APP_MICROSOFT_CLIENT_ID` in your UI environment to enable Microsoft sign-in and account linking.",
+    microsoftLinked: "Linked",
+    microsoftAvailableToLink: "Available to link",
+    microsoftLinkedDate: "Linked {date}",
+    microsoftSignInHint: "Sign in with a Microsoft account that has already been linked to your Jobbjakt user.",
+    continueWithMicrosoft: "Continue with Microsoft",
+    signInWithMicrosoft: "Sign in with Microsoft",
+    linkWithMicrosoft: "Link with Microsoft",
+    microsoftLinkedTo: "Linked to {email}.",
+    microsoftLinkedToYourAccount: "Linked to your Microsoft account.",
+    microsoftBindHint: "Bind a Microsoft account to this user so you can sign in with Microsoft and still keep your normal app roles and data.",
+    microsoftExchangeHint: "Exchange your Microsoft sign-in for a normal Jobbjakt session.",
+    microsoftSignedIn: "Signed in with Microsoft.",
+    microsoftLinkedSuccess: "Microsoft account linked.",
+    microsoftLinkedSuccessWithEmail: "Linked Microsoft account {email}.",
+    microsoftAuthFailed: "Microsoft authentication failed.",
+    microsoftUnlinked: "Microsoft account unlinked.",
+    microsoftUnlinkFailed: "Failed to unlink Microsoft account.",
+    unlinkMicrosoft: "Unlink Microsoft",
     signedOut: "Signed out.",
     signedInAs: "Signed in as {name}.",
     unlinkGoogle: "Unlink Google",
@@ -663,6 +683,7 @@ export const translations = {
     authOptional: "Authentication is optional in this environment.",
     emailAndPassword: "Email & password",
     google: "Google",
+    microsoft: "Microsoft",
     createAccount: "Create account",
     signedIn: "Signed in.",
     rememberMe: "Remember me",
@@ -1572,6 +1593,26 @@ export const translations = {
     googleScriptLoadFailed: "Kunne ikke laste Google-autentiseringsskriptet.",
     googleUnlinked: "Google-konto koblet fra.",
     googleUnlinkFailed: "Kunne ikke koble fra Google-kontoen.",
+    microsoftAccountTitle: "Microsoft-konto",
+    microsoftSetupHint: "Sett `REACT_APP_MICROSOFT_CLIENT_ID` i UI-miljøet ditt for å aktivere Microsoft-innlogging og kontokobling.",
+    microsoftLinked: "Koblet",
+    microsoftAvailableToLink: "Tilgjengelig for kobling",
+    microsoftLinkedDate: "Koblet {date}",
+    microsoftSignInHint: "Logg inn med en Microsoft-konto som allerede er koblet til Jobbjakt-brukeren din.",
+    continueWithMicrosoft: "Fortsett med Microsoft",
+    signInWithMicrosoft: "Logg inn med Microsoft",
+    linkWithMicrosoft: "Koble til med Microsoft",
+    microsoftLinkedTo: "Koblet til {email}.",
+    microsoftLinkedToYourAccount: "Koblet til Microsoft-kontoen din.",
+    microsoftBindHint: "Koble en Microsoft-konto til denne brukeren slik at du kan logge inn med Microsoft og fortsatt beholde vanlige approller og data.",
+    microsoftExchangeHint: "Bytt Microsoft-innloggingen din mot en vanlig Jobbjakt-økt.",
+    microsoftSignedIn: "Logget inn med Microsoft.",
+    microsoftLinkedSuccess: "Microsoft-konto koblet.",
+    microsoftLinkedSuccessWithEmail: "Koblet Microsoft-konto {email}.",
+    microsoftAuthFailed: "Microsoft-autentisering mislyktes.",
+    microsoftUnlinked: "Microsoft-konto koblet fra.",
+    microsoftUnlinkFailed: "Kunne ikke koble fra Microsoft-kontoen.",
+    unlinkMicrosoft: "Koble fra Microsoft",
     signedOut: "Logget ut.",
     signedInAs: "Logget inn som {name}.",
     unlinkGoogle: "Koble fra Google",
@@ -1607,6 +1648,7 @@ export const translations = {
     authOptional: "Autentisering er valgfri i dette miljøet.",
     emailAndPassword: "E-post og passord",
     google: "Google",
+    microsoft: "Microsoft",
     createAccount: "Opprett konto",
     signedIn: "Logget inn.",
     rememberMe: "Husk meg",