[Repo Assist] fix: show hover documentation for FSI hash directives (#r, #load, #nowarn, etc.)

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🤖 This is an automated PR from Repo Assist.

Closes #1225

Root Cause

Hovering over a hash directive like #r, #load, #nowarn returned None (no tooltip shown) for two reasons:

1. Lexer.findLongIdents returns None for multi-character directives like #nowarn — the F# tokenizer emits them as directive tokens, not plain identifier tokens.
2. Even for short directives like #r where an identifier IS found, there was no lookup against the hash-directive description table.

Both code paths fell through to None even though KeywordList.hashDirectives already contained the descriptions needed for completion:

let hashDirectives =
  [ "r", "References an assembly or a nuget: package"
    "nowarn", "Disables a compiler warning or warnings"
    // ...
  ]
```

## Fix

### `KeywordList.fs`

Added `hashDirectiveTooltips`: a dictionary mapping each hash directive key to a synthetic `ToolTipText` built from the existing `hashDirectives` descriptions (same source used for completion item documentation).

### `ParseAndCheckResults.fs` — `TryGetToolTipEnhanced`

Two additions:

1. **In the `findLongIdents = None` branch**: when `findLongIdents` returns `None`, check whether the line starts with `#` and the cursor column is within the directive keyword extent. If so, return the tooltip from `hashDirectiveTooltips`. This handles multi-character directives like `#nowarn`, `#load`, `#light`.

2. **In the `keywordTooltips` fallback**: when `findLongIdents` does find a short identifier but it's not in `keywordTooltips`, check whether the current line starts with `#(ident)`. This handles short directives like `#r` and `#I`.

## Test Status

New test: `verifyDescription 123u 3u` — hover at column 3 of `#nowarn "40"` on the test script returns the expected `"Disables a compiler warning or warnings"` description.

```
Passed: 88 | Failed: 4 | Skipped: 0 | Total: 92

The 4 failures are pre-existing: active pattern ... option(objnull * ...) vs option(obj * ...) — a difference in FCS nullable-annotation rendering unrelated to this change (present on main before this PR).

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