feat: Add human-friendly date parsing to list and summary commands

[kimpepper]

Adds support for date keywords ('today', 'yesterday', 'this week',
'last week', 'this month', 'last month') and YYYY-MM-DD strings to the
--date flag on tl list and tl summary.

• Introduces util.ParseHumanDate backed by the already-vendored
  jinzhu/now library (week starts Monday)
• Replaces FindAllTimeEntries with FindTimeEntriesInRange on the DB
  interface, allowing date-range queries for week/month keywords
• Adds --date flag to tl summary; mutually exclusive with --start/--end
• Removes the hand-rolled startOfCurrentWeek() helper in favour of
  ParseHumanDate("this week", ...)

Co-Authored-By: Claude Sonnet 4.6 noreply@anthropic.com

[Copilot]

Pull request overview

Adds human-friendly --date parsing for tl list and tl summary (keywords + YYYY-MM-DD), and updates the storage layer to support querying by arbitrary date ranges to enable week/month keywords.

Changes:

• Introduces internal/util.ParseHumanDate (keyword + YYYY-MM-DD parsing) backed by github.com/jinzhu/now with Monday week start.
• Replaces single-day DB fetch (FindAllTimeEntries) with range-based fetch (FindTimeEntriesInRange) across repository and mocks.
• Extends tl summary to accept --date (mutually exclusive with --start/--end) and updates tests/examples accordingly.

Reviewed changes

Copilot reviewed 12 out of 13 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
internal/util/dateparse.go	Implements human-friendly date parsing to start/end timestamps + label.
internal/util/dateparse_test.go	Adds unit tests for keywords and YYYY-MM-DD parsing.
internal/db/time_entries.go	Updates DB interface and repository implementation to query entries by date range.
internal/db/repository.go	Removes now-unused day-range helper.
internal/db/mocks/mock_repository.go	Updates mock repository to new range-based API.
cmd/list/command.go	Switches list to ParseHumanDate + range query; updates help text.
cmd/list/command_test.go	Adds coverage for list --date keywords/default/invalid/no entries.
cmd/summary/command.go	Adds --date support, mutual exclusion with --start/--end, and label-based output.
cmd/summary/command_test.go	Adds coverage for summary --date keywords, conflicts, and YYYY-MM-DD.
internal/service/timer_entry_test.go	Updates mock interface implementation to compile with new DB API.
go.mod	Promotes jinzhu/now from indirect to direct dependency.
CLAUDE.md	Adds contributor tooling guidance.
.gitignore	Ignores Claude local settings; reorders .idea.

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