feat: add date filter flags to issue list (#113)

docs/superpowers/specs/2026-04-05-date-filters-design.md

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+# Date Filter Flags for `jr issue list` — Design Spec
+
+> **Issue:** #113 — `issue list: add --created-after and --created-before date filters`
+
+## Problem
+
+`jr issue list` supports `--recent 7d` for relative date filtering but not absolute date ranges. Users who need issues created or updated within a specific date range must use raw JQL:
+
+```bash
+jr issue list --jql 'project = PROJ AND created >= "2026-03-18"'
+```
+
+This requires knowing JQL syntax, which is a knowledge barrier for common queries.
+
+## Solution
+
+Add four convenience flags that generate JQL date clauses:
+
+| Flag | JQL generated | Meaning |
+|------|--------------|---------|
+| `--created-after YYYY-MM-DD` | `created >= "YYYY-MM-DD"` | Issues created on or after this date |
+| `--created-before YYYY-MM-DD` | `created < "YYYY-MM-DD+1"` | Issues created on or before this date |
+| `--updated-after YYYY-MM-DD` | `updated >= "YYYY-MM-DD"` | Issues updated on or after this date |
+| `--updated-before YYYY-MM-DD` | `updated < "YYYY-MM-DD+1"` | Issues updated on or before this date |
+
+### Operator semantics — the midnight problem
+
+JQL interprets date-only values as midnight (00:00:00). This creates a subtle trap:
+
+- `created >= "2026-03-18"` means "from midnight March 18 onwards" — **includes** all of March 18 ✅
+- `created <= "2026-03-18"` means "up to midnight March 18" — **excludes** issues created during March 18 ❌
+
+To give users intuitive "on or before this date" behavior, the `--before` flags add one day and use `<`:
+
+- `--created-before 2026-03-18` generates `created < "2026-03-19"` — includes all of March 18 ✅
+
+The `--after` flags use `>=` directly since midnight-of-date is the correct lower bound.
+
+### Date format
+
+Accept `YYYY-MM-DD` only (ISO 8601 calendar date). Jira JQL also accepts `YYYY/MM/DD` and optional `HH:MM` time, but we accept only the canonical format for simplicity and consistency. Users who need time precision or alternate formats can use `--jql`.
+
+### Validation
+
+Parse dates with `chrono::NaiveDate::parse_from_str(input, "%Y-%m-%d")` before sending to JQL. This catches:
+
+- Invalid format (e.g., `03-18-2026`, `2026/03/18`)
+- Impossible dates (e.g., `2026-02-30`, `2026-13-01`)
+
+Add `validate_date(s: &str) -> Result<NaiveDate, String>` to `jql.rs`. Returns the parsed `NaiveDate` (needed by `--before` flags to compute +1 day). Validation happens early in `handle_list`, same pattern as `--recent`.
+
+### Flag conflicts
+
+| Flag | Conflicts with |
+|------|---------------|
+| `--created-after` | `--recent` (both set a lower bound on `created`) |
+| `--created-before` | (none) |
+| `--updated-after` | (none) |
+| `--updated-before` | (none) |
+
+`--created-after` and `--created-before` do NOT conflict with each other — using both creates a date range. Same for the `--updated-*` pair.
+
+None of the date flags conflict with `--jql`. When combined, date clauses are AND'd with the user's JQL, same as all other filter flags.
+
+### JQL generation
+
+Each flag adds a clause via `build_filter_clauses` in `list.rs`. For `--after` flags, the clause is a simple string interpolation. For `--before` flags, the date is incremented by one day using `chrono::Days::new(1)` and formatted back to `YYYY-MM-DD`.
+
+### Composability
+
+All four flags combine freely with each other and with existing flags:
+
+```bash
+# Date range
+jr issue list --created-after 2026-03-01 --created-before 2026-03-31
+
+# With other filters
+jr issue list --created-after 2026-03-18 --assignee me --open
+
+# Updated date range
+jr issue list --updated-after 2026-03-01 --updated-before 2026-04-01 --status "In Progress"
+```
+
+### Error messages
+
+**Invalid date format:**
+```
+Invalid date "03-18-2026". Expected format: YYYY-MM-DD (e.g., 2026-03-18).
+```
+
+**Impossible date:**
+```
+Invalid date "2026-02-30". Expected format: YYYY-MM-DD (e.g., 2026-03-18).
+```
+
+**Conflict with `--recent`:**
+```
+error: the argument '--created-after <DATE>' cannot be used with '--recent <DURATION>'
+```
+(Clap's automatic conflict error message.)
+
+### Non-interactive / JSON output
+
+No interactive behavior. The flags are fully non-interactive — they take a value and generate JQL. No special JSON output handling needed; the flags only affect which issues are returned.
+
+## Files changed
+
+| File | Change |
+|------|--------|
+| `src/cli/mod.rs` | Add 4 new args to `IssueCommand::List` with `conflicts_with` on `created_after` |
+| `src/jql.rs` | Add `validate_date(s: &str) -> Result<NaiveDate, String>` |
+| `src/cli/issue/list.rs` | Validate dates early, pass to `build_filter_clauses`, add 4 JQL clauses |
+| `tests/cli_smoke.rs` | Smoke test for `--created-after`/`--recent` conflict |
+| `tests/cli_handler.rs` | Handler test for date flags generating correct JQL |
+
+## Out of scope
+
+- Time-of-day precision (`--created-after "2026-03-18 14:30"`) — use `--jql`
+- `YYYY/MM/DD` format — use `--jql`
+- Relative date expressions in these flags (e.g., `--created-after "2 weeks ago"`) — use `--recent`
+- `startOfDay()` / `endOfDay()` JQL functions — the +1 day approach is simpler and equivalent