feat: add all-time variants of productive, language, contribution cards

Four time-bounded cards ("last year") now have all-time counterparts, and
the stats card gains a lifetime commits row.

New cards:
- 6-most-commit-language-all-time.svg (byte-weighted, all lifetime commits)
- 7-productive-time-all-time.svg       (hour histogram over all lifetime commits)
- 8-contributions-all-time.svg         (area chart spanning every active year)

Data pipeline:
- Drop the "since" filter from commitHistoryQuery; FetchProductive now
  paginates unbounded commits and splits each commit into last-year and
  all-time buckets in a single pass — no extra API calls.
- New contributionYearQuery iterates user.contributionYears to
  concatenate calendar data and accumulate TotalCommitsAllTime.
- -commits-per-repo default bumped 100 → 500 to give all-time depth.

Polish:
- Productive-time title embeds the configured tz as "UTC±N.NN" (e.g.
  UTC+7.00) on both last-year and all-time cards.
- Contribution x-axis flipped to mm/yy with an "mm/yy" footer caption
  paralleling productive-time's "hour of day".
- Contribution x-axis label stride now targets ~6 labels regardless of
  bucket count so the all-time chart (~100 months) stays readable while
  the underlying curve still samples every month.

internal/github/queries.go

@@ -24,6 +24,7 @@ query($login: String!, $after: String) {
       contributionTypes: [COMMIT, PULL_REQUEST, ISSUE, PULL_REQUEST_REVIEW]
     ) { totalCount }
     contributionsCollection {
+      contributionYears
       totalCommitContributions
       totalIssueContributions
       totalPullRequestContributions
@@ -69,12 +70,12 @@ query($login: String!, $after: String) {
 // repo, filtered to commits authored by the target user. Used to build the
 // productive-time heatmap.
 const commitHistoryQuery = `
-query($login: String!, $repo: String!, $userId: ID!, $since: GitTimestamp!, $after: String) {
+query($login: String!, $repo: String!, $userId: ID!, $after: String) {
   repository(owner: $login, name: $repo) {
     defaultBranchRef {
       target {
         ... on Commit {
-          history(first: 100, after: $after, author: { id: $userId }, since: $since) {
+          history(first: 100, after: $after, author: { id: $userId }) {
             pageInfo { hasNextPage endCursor }
             nodes { committedDate }
           }
@@ -83,3 +84,23 @@ query($login: String!, $repo: String!, $userId: ID!, $since: GitTimestamp!, $aft
     }
   }
 }`
+
+// contributionYearQuery fetches a single year's contribution calendar days
+// plus the commit total for that year. Looped in Go over user.contributionYears
+// to build the all-time contribution series and lifetime commit count.
+const contributionYearQuery = `
+query($login: String!, $from: DateTime!, $to: DateTime!) {
+  user(login: $login) {
+    contributionsCollection(from: $from, to: $to) {
+      totalCommitContributions
+      contributionCalendar {
+        weeks {
+          contributionDays {
+            contributionCount
+            date
+          }
+        }
+      }
+    }
+  }
+}`