Fixes three bugs reported in #19.

Bug 1 — schedule.max_projects config value ignored by run command

Root cause: runRun() read the --max-projects flag value at startup (defaulting to 1), then never checked cfg.Schedule.MaxProjects after loading config.

Fix:

• Added MaxProjects and MaxTasks fields to ScheduleConfig in config.go (schedule.max_projects, schedule.max_tasks)
• After loading config in runRun(), apply the config value when the CLI flag was not explicitly changed:

  if !maxProjectsChanged && cfg.Schedule.MaxProjects > 0 {
      maxProjects = cfg.Schedule.MaxProjects
  }

Bug 2 — Budget calibration reports "exhausted" at day/week boundary despite 0% usage

Root cause: At a week boundary (midnight, new week starts), the calibrator queries snapshots by week_start and finds 0 rows for the new week. It then falls back to cfg.GetProviderBudget() which is 0 when the user relies on calibration rather than a hardcoded weekly_tokens. A 0-token budget causes the budget calculation to report 0 allowance → provider appears exhausted.

Fix:

• Added loadPreviousWeeklySamples() that queries the prior week's snapshot rows
• When current-week samples are empty, fall back to previous-week data before returning the config default
• Refactored loadClaudeWeeklySamples / loadCodexWeeklySamples to share a common loadWeeklySamplesForWeek() implementation

Bug 3 — Codex provider crashes with exit status 2 in automatic fallback path

Root cause: newCodexAgentFromConfig() always passed WithDangerouslyBypassApprovalsAndSandbox(cfg.Providers.Codex.DangerouslyBypassApprovalsAndSandbox). Since Go's bool zero value is false, an unconfigured Codex provider got bypassPerm=false, stripping --dangerously-bypass-approvals-and-sandbox from the codex exec invocation. Codex requires this flag for non-interactive (headless) execution and exits 2 without it.

Fix:

• Only override the agent's built-in default (true) when the config explicitly enables the flag
• The agent already defaults bypassPerm: true; no-op if the user hasn't configured Codex explicitly

Tests

• TestCalibrateWeekBoundaryFallsBackToPreviousWeek — calibrator uses prior-week data at week boundary
• TestScheduleMaxProjectsFromConfig / TestScheduleMaxProjectsCLIOverridesConfig — config/CLI precedence for max_projects
• TestCodexAgentDefaultsBypassFlag / TestCodexAgentExplicitFalseBypassDisablesFlag — bypass flag behaviour

All existing tests pass (go test ./...).