Restore the typed reset mode and the history controller's own import - #659

Two lines that #641 changed as collateral while PBGitRepository.h still reached Swift
through PBViewController.h. That is no longer the case, so both can go back.

Why the type matters

-Wswitch only checks exhaustiveness on an enum-typed switch. Typing the parameter
NSInteger turned that check off silently. The same function, compiled both ways with the
same case deliberately omitted:

enum parameter, 'Hard' omitted      warning: enumeration value 'Hard' not handled [-Wswitch]
NSInteger parameter, same omission  (silent)

That matters here because the value falls straight into an array literal:

NSString *modeParam;
switch (mode) { case Soft: ...; case Mixed: ...; case Hard: ...; }   // no default
NSArray *arguments = @[ @"reset", modeParam, refName ];

An unhandled mode leaves modeParam nil, and a nil in an array literal raises and takes the
application down, the same way #645, #648 and #654 did.

Not a live crash

There is one caller, PBGitWindowController.m:782, and it passes
GTRepositoryResetTypeSoft. Nothing reaches the gap today. What this restores is the
compile-time guard, so a fourth reset mode fails the build rather than shipping quietly.

The second change has no behavioural effect: PBGitHistoryController.m imports its own
header again instead of relying on it arriving through PBWebHistoryController.h.

Test plan

• 129 tests, 0 failures
• No new warnings from the retyped parameter
• The two compilations above are the evidence for the -Wswitch claim