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/profile.go

@@ -28,12 +28,13 @@ type profileGQL struct {
 		RepositoriesContributedTo struct{ TotalCount int } `json:"repositoriesContributedTo"`
 
 		ContributionsCollection struct {
-			TotalCommitContributions            int `json:"totalCommitContributions"`
-			TotalIssueContributions             int `json:"totalIssueContributions"`
-			TotalPullRequestContributions       int `json:"totalPullRequestContributions"`
-			TotalPullRequestReviewContributions int `json:"totalPullRequestReviewContributions"`
-			TotalRepositoryContributions        int `json:"totalRepositoryContributions"`
-			RestrictedContributionsCount        int `json:"restrictedContributionsCount"`
+			ContributionYears                   []int `json:"contributionYears"`
+			TotalCommitContributions            int   `json:"totalCommitContributions"`
+			TotalIssueContributions             int   `json:"totalIssueContributions"`
+			TotalPullRequestContributions       int   `json:"totalPullRequestContributions"`
+			TotalPullRequestReviewContributions int   `json:"totalPullRequestReviewContributions"`
+			TotalRepositoryContributions        int   `json:"totalRepositoryContributions"`
+			RestrictedContributionsCount        int   `json:"restrictedContributionsCount"`
 			ContributionCalendar                struct {
 				TotalContributions int `json:"totalContributions"`
 				Weeks              []struct {
@@ -107,6 +108,7 @@ func (c *Client) FetchProfile(login string) (*Profile, error) {
 			p.TotalCommits = cc.TotalCommitContributions
 			p.TotalReviews = cc.TotalPullRequestReviewContributions
 			p.TotalContributions = cc.ContributionCalendar.TotalContributions + cc.RestrictedContributionsCount
+			p.ContributionYears = append([]int(nil), cc.ContributionYears...)
 
 			// Flatten week → day into a linear daily series sorted by date.
 			for _, w := range cc.ContributionCalendar.Weeks {