feat(cli): add projects command and sessions --list

[coldhighsun]

Summary

• aimon projects: token usage and estimated cost per project, ordered by --sort tokens|cost|sessions|messages.
• aimon sessions --list: the individual sessions, ordered by --sort tokens|cost|messages|duration|start.
• Both default to the last 30 days and take the date range options (--from/--to, --last, --month), --top, --project, --model and --json. A table gets a Messages column when ordered by messages; the project name is shortened from the left to fit the console width.
• sessions without --list is unchanged; giving it a range, --top, --sort, --project or --model without --list is an error instead of being ignored.
• Core: SessionUsageBuilder aggregates the transcripts per session for a range of local days. A session is identified by the session id on each line, so one resumed across several files is a single session, copied lines are counted once and stay with the original session and project folder (transcripts are named after their session, so a line's home transcript is counted first), and a streamed response is counted once. DataService.GetSessionUsage / GetProjectUsage expose the result.
• Token counting and pricing now live in one place (ModelTokenTotals, TokenUsage.TotalTokens) instead of being copied in each builder.
• Removes the unused SessionParser.ParseSessionSummary / SessionSummary, and corrects the stale GetSessionSummaries text in CLAUDE.md.

Behaviour notes

• Sessions are clipped to the range, so a session that started earlier shows only what happened inside it. messages counts transcript lines (a streamed response is several), and duration is the wall-clock span between the first and last message, idle gaps included.
• For the same days, tokens and messages match aimon month exactly. The cost here prices every message exactly (including 5-minute and 1-hour cache writes), so it differs a little from month, which scales an all-time model mix; month also counts a session once per day it was active.
• --model for sessions counts only the assistant messages of matching models.

Test plan

• dotnet build AIUsageMonitor.slnx (no warnings)
• dotnet test AIUsageMonitor.slnx (388 passed)
• The first commit also builds and passes the Core tests on its own
• Ran projects, sessions --list (--top, --sort, --project, --model, --json, invalid ranges and options) against real local data; tokens and messages reconcile with aimon month for the same days

[codecov]

Codecov Report

❌ Patch coverage is 97.80702% with 10 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...nitor.Core/Providers/Claude/SessionUsageBuilder.cs	94.73%	3 Missing and 3 partials ⚠️
src/AIUsageMonitor.Cli/Program.cs	0.00%	1 Missing ⚠️
...rc/AIUsageMonitor.Cli/Rendering/SpectreRenderer.cs	98.57%	0 Missing and 1 partial ⚠️
...nitor.Core/Providers/Claude/ClaudeUsageProvider.cs	50.00%	1 Missing ⚠️
...nitor.Core/Services/ServiceCollectionExtensions.cs	0.00%	1 Missing ⚠️

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